Image encoding device and image decoding device using triangular prediction mode, and image encoding method and image decoding method performed thereby

ABSTRACT

An image decoding method including: obtaining, from a bitstream, information related to a triangle prediction mode for a current block; splitting the current block into two triangular partitions, according to the information related to a triangle prediction mode; generating a merge list for a triangle prediction mode, according to a merge list generation method in a regular merge mode; selecting a motion vector for the two triangular partitions according to information indicating the motion vector from among motion vectors included in the merge list; obtaining, from a reference image, prediction blocks corresponding to the two triangular partitions, based on the motion vector; and reconstructing the current block, based on a final prediction block.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation Application of U.S. Application No. 17,416,984filed Jun. 21, 2021, which is a National Stage of InternationalApplication No. PCT/KR2019/018217 filed Dec. 20, 2019, which claimsbenefit of U.S. Provisional No. 62/783,662 filed on Dec. 21, 2018 in theUnited States Patent and Trademark Office, the disclosures of which areincorporated herein by reference in their entireties.

TECHNICAL FIELD

The disclosure relates to the fields of image encoding and decoding.More particularly, the disclosure relates to apparatuses for encodingand decoding an image by using a triangle prediction mode, and methodsof encoding and decoding an image by the apparatuses.

BACKGROUND ART

In methods of encoding and decoding an image, respective blocks may beprediction encoded and prediction decoded through inter prediction orintra prediction.

The intra prediction refers to a method of compressing an image bydeleting spatial redundancy in the image, and the inter predictionrefers to a method of compressing an image by deleting temporalredundancy between images. A representative example of theinter-prediction is motion estimation encoding. In the motion estimationencoding, blocks of a current image are predicted by using at least onereference image. A reference block most similar to a current block maybe searched for in a preset search range by using a preset evaluationfunction. The current block is predicted based on the reference block,and a residual block is generated by subtracting a prediction blockgenerated as a result of the prediction from the current block and thenencoded. Here, to further accurately perform the prediction,interpolation may be performed on a reference image so as to generatepixels of a sub pel unit smaller than an integer pel unit, andinter-prediction may be performed based on the pixels of sub pel unit.

In a codec such as H.264 advanced video coding (AVC) and high efficiencyvideo coding (HEVC), a motion vector of pre-encoded blocks adjacent to acurrent block or blocks included in a pre-encoded picture is used as aprediction motion vector of the current block so as to predict a motionvector of the current block. A differential motion vector that is adifference between the motion vector of the current block and theprediction motion vector is signaled to a decoder according to a presetscheme. In a merge mode of inter prediction, instead of the differentialmotion vector being signaled to the decoder, information indicating amotion vector candidate to be used as a motion vector of a current blockfrom among motion vector candidates included in a merge list generatedaccording to a preset rule is signaled to the decoder.

DESCRIPTION OF EMBODIMENTS Technical Problem

According to a technical objective, an image decoding apparatus andmethod and an image encoding apparatus and method according to anembodiment may set restrictions on a prediction mode of a current block,thereby preventing unnecessary information from being included in abitstream.

Also, according to a technical objective, an image decoding apparatusand method and an image encoding apparatus and method according to anembodiment may simplify a process of encoding and decoding an image.

Solution to Problem

According to an embodiment, an image decoding method may include:obtaining, from a bitstream, information related to a triangleprediction mode for a current block split from an image; splitting thecurrent block into two triangular partitions, according to theinformation related to a triangle prediction mode; generating a mergelist for the triangle prediction mode, according to a merge listgeneration method in a regular merge mode in which the current block isreconstructed without being split into triangular partitions; selectinga motion vector for the two triangular partitions according toinformation indicating the motion vector from among motion vectorsincluded in the merge list, the information being included in theinformation related to a triangle prediction mode; obtaining, from areference image, prediction blocks corresponding to the two triangularpartitions, based on the selected motion vector; and reconstructing thecurrent block, based on a final prediction block obtained as acombination of the prediction blocks.

Advantageous Effects of Disclosure

According to an embodiment, an image decoding apparatus and method, andan image encoding apparatus and method may set restrictions on aprediction mode of a current block, thereby preventing unnecessaryinformation from being included in a bitstream.

Also, according to an embodiment, an image decoding apparatus andmethod, and an image encoding apparatus and method may simplify aprocess of encoding and decoding an image.

However, effects achievable by an apparatus and method for decoding animage, and an apparatus and method for encoding an image, according toan embodiment, are not limited to those mentioned above, and othereffects that not mentioned could be clearly understood by one ofordinary skill in the art from the following descriptions.

BRIEF DESCRIPTION OF DRAWINGS

A brief description of each drawing is provided for better understandingof the drawings cited herein.

FIG. 1 is a block diagram of an image decoding apparatus according to anembodiment.

FIG. 2 is a block diagram of an image encoding apparatus according to anembodiment.

FIG. 3 illustrates a process, performed by an image decoding apparatus,of determining at least one coding unit by splitting a current codingunit, according to an embodiment.

FIG. 4 illustrates a process, performed by an image decoding apparatus,of determining at least one coding unit by splitting a non-square codingunit, according to an embodiment.

FIG. 5 illustrates a process, performed by an image decoding apparatus,of splitting a coding unit based on at least one of block shapeinformation and split shape mode information, according to anembodiment.

FIG. 6 illustrates a method, performed by an image decoding apparatus,of determining a preset coding unit from among an odd number of codingunits, according to an embodiment.

FIG. 7 illustrates an order of processing a plurality of coding unitswhen an image decoding apparatus determines the plurality of codingunits by splitting a current coding unit, according to an embodiment.

FIG. 8 illustrates a process, performed by an image decoding apparatus,of determining that a current coding unit is to be split into an oddnumber of coding units, when the coding units are not processable in apreset order, according to an embodiment.

FIG. 9 illustrates a process, performed by an image decoding apparatus,of determining at least one coding unit by splitting a first codingunit, according to an embodiment.

FIG. 10 illustrates that a shape into which a second coding unit issplittable is restricted when the second coding unit having a non-squareshape, which is determined when an image decoding apparatus splits afirst coding unit, satisfies a preset condition, according to anembodiment.

FIG. 11 illustrates a process, performed by an image decoding apparatus,of splitting a square coding unit when split shape mode informationindicates that the square coding unit is to not be split into foursquare coding units, according to an embodiment.

FIG. 12 illustrates that a processing order between a plurality ofcoding units may be changed depending on a process of splitting a codingunit, according to an embodiment.

FIG. 13 illustrates a process of determining a depth of a coding unit asa shape and size of the coding unit change, when the coding unit isrecursively split such that a plurality of coding units are determined,according to an embodiment.

FIG. 14 illustrates depths that are determinable based on shapes andsizes of coding units, and part indexes (PIDs) that are fordistinguishing the coding units, according to an embodiment.

FIG. 15 illustrates that a plurality of coding units are determinedbased on a plurality of preset data units included in a picture,according to an embodiment.

FIG. 16 illustrates a processing block serving as a unit for determininga determination order of reference coding units included in a picture,according to an embodiment.

FIG. 17 illustrates coding units that are determinable for each ofpictures when a split shape combination for a coding unit varies foreach picture, according to an embodiment.

FIG. 18 illustrates various shapes of a coding unit which may bedetermined based on split shape mode information that can be representedas a binary code, according to an embodiment.

FIG. 19 illustrates other shapes of a coding unit which may bedetermined based on split shape mode information that can be representedas a binary code, according to an embodiment.

FIG. 20 is a block diagram of an image encoding and decoding system thatperforms loop filtering.

FIG. 21 is a block diagram illustrating a configuration of an imagedecoding apparatus according to an embodiment.

FIG. 22 illustrates an example of a syntax structure for parsinginformation related to a triangle prediction mode, according to anembodiment.

FIG. 23 is a diagram for describing a merge list generation method in aregular merge mode.

FIG. 24 illustrates an example for describing a method of generating amerge list for a triangle prediction mode from a merge list for aregular merge mode.

FIG. 25 illustrates an example for describing a method of generating amerge list for a triangle prediction mode from a merge list for aregular merge mode.

FIG. 26 is a diagram for describing a method of determining predictionblocks corresponding to two triangular partitions split from a currentblock.

FIG. 27 is a diagram for describing a method of generating a finalprediction block by combining prediction blocks corresponding to twotriangular partitions.

FIG. 28 is a flowchart of an image decoding method according to anembodiment.

FIG. 29 is a block diagram of a configuration of an image encodingapparatus according to an embodiment.

FIG. 30 is a flowchart of an image encoding method according to anembodiment.

BEST MODE

According to an embodiment, an image decoding method may include:obtaining, from a bitstream, information related to a triangleprediction mode for a current block split from an image; splitting thecurrent block into two triangular partitions, according to theinformation related to a triangle prediction mode; generating a mergelist for the triangle prediction mode, according to a merge listgeneration method in a regular merge mode in which the current block isreconstructed without being split into triangular partitions; selectinga motion vector for the two triangular partitions according toinformation indicating the motion vector from among motion vectorsincluded in the merge list, the information being included in theinformation related to a triangle prediction mode; obtaining, from areference image, prediction blocks corresponding to the two triangularpartitions, based on the selected motion vector; and reconstructing thecurrent block, based on a final prediction block obtained as acombination of the prediction blocks.

In an embodiment, the merge list generation method in the regular mergemode may be a method of generating a merge list including motion vectorsof blocks that are available from among spatial blocks being spatiallyrelated to the current block and temporal blocks being temporallyrelated to the current block.

The obtaining of, from the bitstream, the information related to atriangle prediction mode may include: comparing a size of the currentblock with a first threshold value; and when a result of the comparingsatisfies a preset condition, obtaining, from the bitstream, theinformation related to a triangle prediction mode for the current block.

The obtaining of, from the bitstream, the information related to atriangle prediction mode may include: when a height of the current blockis smaller than the first threshold value and a width of the currentblock is smaller than the first threshold value, obtaining theinformation related to a triangle prediction mode from the bitstream.

The comparing may include comparing the size of the current block with asecond threshold value, and the obtaining of, from the bitstream, theinformation related to a triangle prediction mode may include: when theresult of the comparing between the size of the current block and thefirst threshold value, and a result of the comparing between the size ofthe current block and the second threshold value satisfy the presetcondition, obtaining the information related to a triangle predictionmode from the bitstream.

The comparing of the size of the current block with the second thresholdvalue may include comparing a value obtained by multiplying a height ofthe current block by a width of the current block with the secondthreshold value.

The first threshold value may be greater than the second thresholdvalue.

The obtaining of, from the bitstream, the information related to atriangle prediction mode may include, when a prediction mode of thecurrent block is not an inter-intra combination mode, obtaining theinformation related to a triangle prediction mode from the bitstream.

When a prediction mode of the current block is a merge mode using adifferential motion vector, the information related to a triangleprediction mode may not be obtained from the bitstream, and the imagedecoding method may further include reconstructing the current blockaccording to the merge mode using a differential motion vector.

The reconstructing of the current block may include generating the finalprediction block according to a weighted sum of sample values includedin prediction blocks respectively corresponding to the two triangularpartitions.

The splitting of the current block into the two triangular partitionsmay include splitting the current block from an upper-left corner of thecurrent block toward a lower-right corner of the current block, orsplitting the current block from an upper-right corner of the currentblock toward a lower-left corner of the current block.

According to an embodiment, an image decoding apparatus may include: anentropy decoder configured to obtain, from a bitstream, informationrelated to a triangle prediction mode for a current block split from animage; and a prediction decoder configured to split the current blockinto two triangular partitions, according to the information related toa triangle prediction mode, generate a merge list for a triangleprediction mode, according to a merge list generation method in aregular merge mode in which the current block is reconstructed withoutbeing split into triangular partitions, select a motion vector for thetwo triangular partitions according to information indicating the motionvector from among motion vectors included in the merge list, theinformation being included in the information related to a triangleprediction mode, obtain, from a reference image, prediction blockscorresponding to the two triangular partitions, based on the selectedmotion vector, and reconstruct the current block, based on a finalprediction block obtained as a combination of the prediction blocks.

According to an embodiment, an image encoding method may include:determining a prediction mode of a current block to be a triangleprediction mode, the current block being split from an image; splittingthe current block into two triangular partitions; generating a mergelist for the triangle prediction mode, according to a merge listgeneration method in a regular merge mode in which the current block isreconstructed without being split into triangular partitions; selectinga motion vector for the two triangular partitions from among motionvectors included in the merge list; and generating a bitstream includinginformation related to a triangle prediction mode including informationindicating the selected motion vector.

The determining of the prediction mode of the current block to be thetriangle prediction mode may include: comparing a size of the currentblock with a first threshold value; and when a result of the comparingsatisfies a preset condition, determining the prediction mode of thecurrent block to be the triangle prediction mode.

MODE OF DISCLOSURE

As the disclosure allows for various changes and numerous examples,particular embodiments will be illustrated in the drawings and describedin detail in the written descriptions. However, this is not intended tolimit the disclosure to particular modes of practice, and it will beunderstood that all changes, equivalents, and substitutes that do notdepart from the spirit and technical scope of various embodiments areencompassed in the disclosure.

In the description of embodiments, certain detailed explanations ofrelated art are omitted when it is deemed that they may unnecessarilyobscure the essence of the disclosure. Also, numbers (for example, afirst, a second, and the like) used in the description of thespecification are merely identifier codes for distinguishing one elementfrom another.

Also, in the present specification, it will be understood that whenelements are “connected” or “coupled” to each other, the elements may bedirectly connected or coupled to each other, but may alternatively beconnected or coupled to each other with an intervening elementtherebetween, unless specified otherwise.

In the present specification, regarding an element represented as a“unit” or a “module”, two or more elements may be combined into oneelement or one element may be divided into two or more elementsaccording to subdivided functions. In addition, each element describedhereinafter may additionally perform some or all of functions performedby another element, in addition to main functions of itself, and some ofthe main functions of each element may be performed entirely by anotherelement.

Also, in the present specification, an “image” or a “picture” mayindicate a static image. Alternatively, the “image” or the “picture” mayindicate each frame constituting a video, or the video itself.

Also, in the present specification, a “sample” or a “signal” indicatesdata allocated to a sampling position of an image, i.e., data to beprocessed. For example, in an image, pixel values in a spatial domainand transform coefficients on a transform domain may be samples. A unitincluding at least one such sample may be defined as a block.

Hereinafter, with reference to FIGS. 1 to 20 , provided are an imageencoding method and apparatus therefor and an image decoding method andapparatus therefor based on coding units and transform units of a treestructure according to an embodiment.

FIG. 1 illustrates a block diagram of an image decoding apparatus 100according to an embodiment.

The image decoding apparatus 100 may include a bitstream obtainer 110and a decoder 120. The bitstream obtainer 110 and the decoder 120 mayinclude at least one processor. Also, the bitstream obtainer 110 and thedecoder 120 may include a memory storing instructions to be performed bythe at least one processor.

The bitstream obtainer 110 may receive a bitstream. The bitstreamincludes information of an image encoded by an image encoding apparatus200 described below. Also, the bitstream may be transmitted from theimage encoding apparatus 200. The image encoding apparatus 200 and theimage decoding apparatus 100 may be connected by wire or wirelessly, andthe bitstream obtainer 110 may receive the bitstream by wire orwirelessly. The bitstream obtainer 110 may receive the bitstream from astorage medium, such as an optical medium or a hard disk. The decoder120 may reconstruct an image based on information obtained from thereceived bitstream. The decoder 120 may obtain, from the bitstream, asyntax element for reconstructing the image. The decoder 120 mayreconstruct the image based on the syntax element.

In further descriptions of operations of the image decoding apparatus100, the bitstream obtainer 110 may receive a bitstream.

The image decoding apparatus 100 may perform an operation of obtaining,from the bitstream, a bin string corresponding to a split shape mode ofa coding unit. The image decoding apparatus 100 may perform an operationof determining a split rule of the coding unit. Also, the image decodingapparatus 100 may perform an operation of splitting the coding unit intoa plurality of coding units, based on at least one of the bin stringcorresponding to the split shape mode and the split rule. The imagedecoding apparatus 100 may determine an allowable first range of a sizeof the coding unit, according to a ratio of the width and the height ofthe coding unit, so as to determine the split rule. The image decodingapparatus 100 may determine an allowable second range of the size of thecoding unit, according to the split shape mode of the coding unit, so asto determine the split rule.

Hereinafter, splitting of a coding unit will be described in detailaccording to an embodiment of the disclosure.

First, one picture may be split into one or more slices or one or moretiles. One slice or one tile may be a sequence of one or more largestcoding units (coding tree units (CTUs)). There is a largest coding block(coding tree block (CTB)) conceptually compared to a largest coding unit(CTU).

The largest coding block (CTB) denotes an N×N block including N×Nsamples (where N is an integer). Each color component may be split intoone or more largest coding blocks.

When a picture has three sample arrays (sample arrays for Y, Cr, and Cbcomponents), a largest coding unit (CTU) includes a largest coding blockof a luma sample, two corresponding largest coding blocks of chromasamples, and syntax structures used to encode the luma sample and thechroma samples. When a picture is a monochrome picture, a largest codingunit includes a largest coding block of a monochrome sample and syntaxstructures used to encode the monochrome samples. When a picture is apicture encoded in color planes separated according to color components,a largest coding unit includes syntax structures used to encode thepicture and samples of the picture.

One largest coding block (CTB) may be split into M×N coding blocksincluding M×N samples (M and N are integers).

When a picture has sample arrays for Y, Cr, and Cb components, a codingunit (CU) includes a coding block of a luma sample, two correspondingcoding blocks of chroma samples, and syntax structures used to encodethe luma sample and the chroma samples. When a picture is a monochromepicture, a coding unit includes a coding block of a monochrome sampleand syntax structures used to encode the monochrome samples. When apicture is a picture encoded in color planes separated according tocolor components, a coding unit includes syntax structures used toencode the picture and samples of the picture.

As described above, a largest coding block and a largest coding unit areconceptually distinguished from each other, and a coding block and acoding unit are conceptually distinguished from each other. That is, a(largest) coding unit refers to a data structure including a (largest)coding block including a corresponding sample and a syntax structurecorresponding to the (largest) coding block. However, because it isunderstood by one of ordinary skill in the art that a (largest) codingunit or a (largest) coding block refers to a block of a preset sizeincluding a preset number of samples, a largest coding block and alargest coding unit, or a coding block and a coding unit are mentionedin the following specification without being distinguished unlessotherwise described.

An image may be split into largest coding units (CTUs). A size of eachlargest coding unit may be determined based on information obtained froma bitstream. A shape of each largest coding unit may be a square shapeof the same size. However, the embodiment is not limited thereto.

For example, information about a maximum size of a luma coding block maybe obtained from a bitstream. For example, the maximum size of the lumacoding block indicated by the information about the maximum size of theluma coding block may be one of 4×4, 8×8, 16×16, 32×32, 64×64, 128×128,and 256×256.

For example, information about a luma block size difference and amaximum size of a luma coding block that may be split into two may beobtained from a bitstream. The information about the luma block sizedifference may refer to a size difference between a luma largest codingunit and a largest luma coding block that may be split into two.Accordingly, when the information about the maximum size of the lumacoding block that may be split into two and the information about theluma block size difference obtained from the bitstream are combined witheach other, a size of the luma largest coding unit may be determined. Asize of a chroma largest coding unit may be determined by using the sizeof the luma largest coding unit. For example, when a Y:Cb:Cr ratio is4:2:0 according to a color format, a size of a chroma block may be halfa size of a luma block, and a size of a chroma largest coding unit maybe half a size of a luma largest coding unit.

According to an embodiment, because information about a maximum size ofa luma coding block that is binary splittable is obtained from abitstream, the maximum size of the luma coding block that is binarysplittable may be variably determined. In contrast, a maximum size of aluma coding block that is ternary splittable may be fixed. For example,the maximum size of the luma coding block that is ternary splittable inan I-slice may be 32×32, and the maximum size of the luma coding blockthat is ternary splittable in a P-slice or a B-slice may be 64×64.

Also, a largest coding unit may be hierarchically split into codingunits based on split shape mode information obtained from a bitstream.At least one of information indicating whether quad splitting isperformed, information indicating whether multi-splitting is performed,split direction information, and split type information may be obtainedas the split shape mode information from the bitstream.

For example, the information indicating whether quad splitting isperformed may indicate whether a current coding unit is quad split(QUAD_SPLIT) or not.

When the current coding unit is not quad split, the informationindicating whether multi-splitting is performed may indicate whether thecurrent coding unit is no longer split (NO_SPLIT) or binary/ternarysplit.

When the current coding unit is binary split or ternary split, the splitdirection information indicates that the current coding unit is split inone of a horizontal direction and a vertical direction.

When the current coding unit is split in the horizontal direction or thevertical direction, the split type information indicates that thecurrent coding unit is binary split or ternary split.

A split mode of the current coding unit may be determined according tothe split direction information and the split type information. A splitmode when the current coding unit is binary split in the horizontaldirection may be determined to be a binary horizontal split mode(SPLIT_BT_HOR), a split mode when the current coding unit is ternarysplit in the horizontal direction may be determined to be a ternaryhorizontal split mode (SPLIT_TT_HOR), a split mode when the currentcoding unit is binary split in the vertical direction may be determinedto be a binary vertical split mode (SPLIT_BT_VER), and a split mode whenthe current coding unit is ternary split in the vertical direction maybe determined to be a ternary vertical split mode (SPLIT_TT_VER).

The image decoding apparatus 100 may obtain, from the bitstream, thesplit shape mode information from one bin string. A form of thebitstream received by the image decoding apparatus 100 may include fixedlength binary code, unary code, truncated unary code, predeterminedbinary code, or the like. The bin string is information in a binarynumber. The bin string may include at least one bit. The image decodingapparatus 100 may obtain the split shape mode information correspondingto the bin string, based on the split rule. The image decoding apparatus100 may determine whether to quad split a coding unit, whether not tosplit a coding unit, a split direction, and a split type, based on onebin string.

The coding unit may be smaller than or the same as the largest codingunit. For example, because a largest coding unit is a coding unit havinga maximum size, the largest coding unit is one of coding units. Whensplit shape mode information about a largest coding unit indicates thatsplitting is not performed, a coding unit determined in the largestcoding unit has the same size as that of the largest coding unit. Whensplit shape mode information about a largest coding unit indicates thatsplitting is performed, the largest coding unit may be split into codingunits. Also, when split shape mode information about a coding unitindicates that splitting is performed, the coding unit may be split intosmaller coding units. However, the splitting of the image is not limitedthereto, and the largest coding unit and the coding unit may not bedistinguished. The splitting of the coding unit will be described indetail with reference to FIGS. 3 to 16 .

Also, one or more prediction blocks for prediction may be determinedfrom a coding unit. The prediction block may be the same as or smallerthan the coding unit. Also, one or more transform blocks fortransformation may be determined from a coding unit. The transform blockmay be equal to or smaller than the coding unit.

The shapes and sizes of the transform block and prediction block may notbe related to each other.

In another embodiment, prediction may be performed by using a codingunit as a prediction unit. Also, transformation may be performed byusing a coding unit as a transform block.

The splitting of the coding unit will be described in detail withreference to FIGS. 3 to 16 . A current block and an adjacent block ofthe disclosure may indicate one of the largest coding unit, the codingunit, the prediction block, and the transform block. Also, the currentblock of the current coding unit is a block that is currently beingdecoded or encoded or a block that is currently being split. Theadjacent block may be a block reconstructed before the current block.The adjacent block may be adjacent to the current block spatially ortemporally. The adjacent block may be located at one of the lower left,left, upper left, top, upper right, right, lower right of the currentblock.

FIG. 3 illustrates a process, performed by the image decoding apparatus100, of determining at least one coding unit by splitting a currentcoding unit, according to an embodiment.

A block shape may include 4N×4N, 4N×2N, 2N×4N, 4N×N, N×4N, 32N×N, N×32N,16N×N, N×16N, 8N×N, or N×8N. Here, N may be a positive integer. Blockshape information is information indicating at least one of a shape, adirection, a ratio of width and height, or size of a coding unit.

The shape of the coding unit may include a square and a non-square. Whenthe lengths of the width and height of the coding unit are the same(i.e., when the block shape of the coding unit is 4N×4N), the imagedecoding apparatus 100 may determine the block shape information of thecoding unit as a square. The image decoding apparatus 100 may determinethe shape of the coding unit to be a non-square.

When the width and the height of the coding unit are different from eachother (i.e., when the block shape of the coding unit is 4N×2N, 2N×4N,4N×N, N×4N, 32N×N, N×32N, 16N×N, N×16N, 8N×N, or N×8N), the imagedecoding apparatus 100 may determine the block shape information of thecoding unit as a non-square shape. When the shape of the coding unit isnon-square, the image decoding apparatus 100 may determine the ratio ofthe width and height among the block shape information of the codingunit to be at least one of 1:2, 2:1, 1:4, 4:1, 1:8, 8:1, 1:16, 16:1,1:32, and 32:1. Also, the image decoding apparatus 100 may determinewhether the coding unit is in a horizontal direction or a verticaldirection, based on the length of the width and the length of the heightof the coding unit. Also, the image decoding apparatus 100 may determinethe size of the coding unit, based on at least one of the length of thewidth, the length of the height, or the area of the coding unit.

According to an embodiment, the image decoding apparatus 100 maydetermine the shape of the coding unit by using the block shapeinformation, and may determine a splitting method of the coding unit byusing the split shape mode information. That is, a coding unit splittingmethod indicated by the split shape mode information may be determinedbased on a block shape indicated by the block shape information used bythe image decoding apparatus 100.

The image decoding apparatus 100 may obtain the split shape modeinformation from a bitstream. However, an embodiment is not limitedthereto, and the image decoding apparatus 100 and the image encodingapparatus 200 may determine pre-agreed split shape mode information,based on the block shape information. The image decoding apparatus 100may determine the pre-agreed split shape mode information with respectto a largest coding unit or a minimum coding unit. For example, theimage decoding apparatus 100 may determine split shape mode informationwith respect to the largest coding unit to be a quad split. Also, theimage decoding apparatus 100 may determine split shape mode informationregarding the smallest coding unit to be “not to perform splitting”. Inparticular, the image decoding apparatus 100 may determine the size ofthe largest coding unit to be 256×256. The image decoding apparatus 100may determine the pre-agreed split shape mode information to be a quadsplit. The quad split is a split shape mode in which the width and theheight of the coding unit are both bisected. The image decodingapparatus 100 may obtain a coding unit of a 128×128 size from thelargest coding unit of a 256×256 size, based on the split shape modeinformation. Also, the image decoding apparatus 100 may determine thesize of the smallest coding unit to be 4×4. The image decoding apparatus100 may obtain split shape mode information indicating “not to performsplitting” with respect to the smallest coding unit.

According to an embodiment, the image decoding apparatus 100 may use theblock shape information indicating that the current coding unit has asquare shape. For example, the image decoding apparatus 100 maydetermine whether not to split a square coding unit, whether tovertically split the square coding unit, whether to horizontally splitthe square coding unit, or whether to split the square coding unit intofour coding units, based on the split shape mode information. Referringto FIG. 3 , when the block shape information of a current coding unit300 indicates a square shape, the decoder 120 may not split a codingunit 310 a having the same size as the current coding unit 300, based onthe split shape mode information indicating not to perform splitting, ormay determine coding units 310 b, 310 c, 310 d, 310 e, or 310 f splitbased on the split shape mode information indicating a preset splittingmethod.

Referring to FIG. 3 , according to an embodiment, the image decodingapparatus 100 may determine two coding units 310 b obtained by splittingthe current coding unit 300 in a vertical direction, based on the splitshape mode information indicating to perform splitting in a verticaldirection. The image decoding apparatus 100 may determine two codingunits 310 c obtained by splitting the current coding unit 300 in ahorizontal direction, based on the split shape mode informationindicating to perform splitting in a horizontal direction. The imagedecoding apparatus 100 may determine four coding units 310 d obtained bysplitting the current coding unit 300 in vertical and horizontaldirections, based on the split shape mode information indicating toperform splitting in vertical and horizontal directions. According to anembodiment, the image decoding apparatus 100 may determine three codingunits 310 e obtained by splitting the current coding unit 300 in avertical direction, based on the split shape mode information indicatingto perform ternary splitting in a vertical direction. The image decodingapparatus 100 may determine three coding units 310 f obtained bysplitting the current coding unit 300 in a horizontal direction, basedon the split shape mode information indicating to perform ternarysplitting in a horizontal direction. However, splitting methods of thesquare coding unit are not limited to the above-described methods, andthe split shape mode information may indicate various methods. Presetsplitting methods of splitting the square coding unit will be describedin detail below in relation to various embodiments.

FIG. 4 illustrates a process, performed by the image decoding apparatus100, of determining at least one coding unit by splitting a non-squarecoding unit, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 may useblock shape information indicating that a current coding unit has anon-square shape. The image decoding apparatus 100 may determine whethernot to split the non-square current coding unit or whether to split thenon-square current coding unit by using a preset splitting method, basedon split shape mode information. Referring to FIG. 4 , when the blockshape information of a current coding unit 400 or 450 indicates anon-square shape, the image decoding apparatus 100 may determine acoding unit 410 or 460 having the same size as the current coding unit400 or 450, based on the split shape mode information indicating not toperform splitting, or may determine coding units 420 a and 420 b, 430 ato 430 c, 470 a and 470 b, or 480 a to 480 c split based on the splitshape mode information indicating a preset splitting method. Presetsplitting methods of splitting a non-square coding unit will bedescribed in detail below in relation to various embodiments.

According to an embodiment, the image decoding apparatus 100 maydetermine a splitting method of a coding unit by using the split shapemode information and, in this case, the split shape mode information mayindicate the number of one or more coding units generated by splitting acoding unit. Referring to FIG. 4 , when the split shape mode informationindicates to split the current coding unit 400 or 450 into two codingunits, the image decoding apparatus 100 may determine two coding units420 a and 420 b, or 470 a and 470 b included in the current coding unit400 or 450, by splitting the current coding unit 400 or 450 based on thesplit shape mode information.

According to an embodiment, when the image decoding apparatus 100 splitsthe non-square current coding unit 400 or 450 based on the split shapemode information, the image decoding apparatus 100 may consider thelocation of a long side of the non-square current coding unit 400 or 450to split a current coding unit. For example, the image decodingapparatus 100 may determine a plurality of coding units by splitting thecurrent coding unit 400 or 450 in a direction of splitting a long sideof the current coding unit 400 or 450, in consideration of the shape ofthe current coding unit 400 or 450.

According to an embodiment, when the split shape mode informationindicates to split (ternary split) a coding unit into an odd number ofblocks, the image decoding apparatus 100 may determine an odd number ofcoding units included in the current coding unit 400 or 450. Forexample, when the split shape mode information indicates to split thecurrent coding unit 400 or 450 into three coding units, the imagedecoding apparatus 100 may split the current coding unit 400 or 450 intothree coding units 430 a, 430 b, and 430 c, or 480 a, 480 b, and 480 c.

According to an embodiment, a ratio of the width and height of thecurrent coding unit 400 or 450 may be 4:1 or 1:4. When the ratio of thewidth and height is 4:1, the block shape information may indicate ahorizontal direction because the length of the width is longer than thelength of the height. When the ratio of the width and height is 1:4, theblock shape information may indicate a vertical direction because thelength of the width is shorter than the length of the height. The imagedecoding apparatus 100 may determine to split a current coding unit intoan odd number of blocks, based on the split shape mode information.Also, the image decoding apparatus 100 may determine a split directionof the current coding unit 400 or 450, based on the block shapeinformation of the current coding unit 400 or 450. For example, when thecurrent coding unit 400 is in the vertical direction, the image decodingapparatus 100 may determine the coding units 430 a, 430 b, and 430 c bysplitting the current coding unit 400 in the horizontal direction. Also,when the current coding unit 450 is in the horizontal direction, theimage decoding apparatus 100 may determine the coding units 480 a, 480b, and 480 c by splitting the current coding unit 450 in the verticaldirection.

According to an embodiment, the image decoding apparatus 100 maydetermine an odd number of coding units included in the current codingunit 400 or 450, and not all the determined coding units may have thesame size. For example, a preset coding unit 430 b or 480 b from amongthe determined odd number of coding units 430 a, 430 b, and 430 c, or480 a, 480 b, and 480 c may have a size different from the size of theother coding units 430 a and 430 c, or 480 a and 480 c. That is, codingunits which may be determined by splitting the current coding unit 400or 450 may have multiple sizes and, in some cases, all of the odd numberof coding units 430 a, 430 b, and 430 c, or 480 a, 480 b, and 480 c mayhave different sizes.

According to an embodiment, when the split shape mode informationindicates to split a coding unit into the odd number of blocks, theimage decoding apparatus 100 may determine the odd number of codingunits included in the current coding unit 400 or 450, and moreover, mayput a preset restriction on at least one coding unit from among the oddnumber of coding units generated by splitting the current coding unit400 or 450. Referring to FIG. 4 , the image decoding apparatus 100 mayset a decoding process regarding the coding unit 430 b or 480 b locatedat the center among the three coding units 430 a, 430 b, and 430 c, or480 a, 480 b, and 480 c generated as the current coding unit 400 or 450is split to be different from that of the other coding units 430 a and430 c, or 480 a and 480 c. For example, the image decoding apparatus 100may restrict the coding unit 430 b or 480 b at the center location to beno longer split or to be split only a preset number of times, unlike theother coding units 430 a and 430 c, or 480 a and 480 c.

FIG. 5 illustrates a process, performed by the image decoding apparatus100, of splitting a coding unit based on at least one of block shapeinformation and split shape mode information, according to anembodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine to split or to not split a square first coding unit 500 intocoding units, based on at least one of the block shape information andthe split shape mode information. According to an embodiment, when thesplit shape mode information indicates to split the first coding unit500 in a horizontal direction, the image decoding apparatus 100 maydetermine a second coding unit 510 by splitting the first coding unit500 in a horizontal direction. A first coding unit, a second codingunit, and a third coding unit used according to an embodiment are termsused to understand a relation before and after splitting a coding unit.For example, a second coding unit may be determined by splitting a firstcoding unit, and a third coding unit may be determined by splitting thesecond coding unit. It will be understood that the relation of the firstcoding unit, the second coding unit, and the third coding unit followsthe above descriptions.

According to an embodiment, the image decoding apparatus 100 maydetermine to split or to not split the determined second coding unit 510into coding units, based on the split shape mode information. Referringto FIG. 5 , the image decoding apparatus 100 may split the non-squaresecond coding unit 510, which is determined by splitting the firstcoding unit 500, into one or more third coding units 520 a, 520 b, 520c, and 520 d based on at least one of the split shape mode informationand the split shape mode information, or may not split the non-squaresecond coding unit 510. The image decoding apparatus 100 may obtain thesplit shape mode information, and may obtain a plurality ofvarious-shaped second coding units (e.g., 510) by splitting the firstcoding unit 500, based on the obtained split shape mode information, andthe second coding unit 510 may be split by using a splitting method ofthe first coding unit 500 based on the split shape mode information.According to an embodiment, when the first coding unit 500 is split intothe second coding units 510 based on the split shape mode information ofthe first coding unit 500, the second coding unit 510 may also be splitinto the third coding units (e.g., 520 a, or 520 b, 520 c, and 520 d)based on the split shape mode information of the second coding unit 510.That is, a coding unit may be recursively split based on the split shapemode information of each coding unit. Therefore, a square coding unitmay be determined by splitting a non-square coding unit, and anon-square coding unit may be determined by recursively splitting thesquare coding unit.

Referring to FIG. 5 , a preset coding unit (e.g., a coding unit locatedat a center location, or a square coding unit) from among an odd numberof third coding units 520 b, 520 c, and 520 d determined by splittingthe non-square second coding unit 510 may be recursively split.According to an embodiment, the square third coding unit 520 c fromamong the odd number of third coding units 520 b, 520 c, and 520 d maybe split in a horizontal direction into a plurality of fourth codingunits. A non-square fourth coding unit 530 b or 530 d from among theplurality of fourth coding units 530 a, 530 b, 530 c, and 530 d may bere-split into a plurality of coding units. For example, the non-squarefourth coding unit 530 b or 530 d may be re-split into an odd number ofcoding units. A method that may be used to recursively split a codingunit will be described below in relation to various embodiments.

According to an embodiment, the image decoding apparatus 100 may spliteach of the third coding units 520 a, or 520 b, 520 c, and 520 d intocoding units, based on the split shape mode information. Also, the imagedecoding apparatus 100 may determine to not split the second coding unit510 based on the split shape mode information. According to anembodiment, the image decoding apparatus 100 may split the non-squaresecond coding unit 510 into the odd number of third coding units 520 b,520 c, and 520 d. The image decoding apparatus 100 may put a presetrestriction on a preset third coding unit from among the odd number ofthird coding units 520 b, 520 c, and 520 d. For example, the imagedecoding apparatus 100 may restrict the third coding unit 520 c at acenter location from among the odd number of third coding units 520 b,520 c, and 520 d to be no longer split or to be split a settable numberof times.

Referring to FIG. 5 , the image decoding apparatus 100 may restrict thethird coding unit 520 c, which is at the center location from among theodd number of third coding units 520 b, 520 c, and 520 d included in thenon-square second coding unit 510, to be no longer split, to be split byusing a preset splitting method (e.g., split into only four coding unitsor split by using a splitting method of the second coding unit 510), orto be split only a preset number of times (e.g., split only n times(where n>0)). However, the restrictions on the third coding unit 520 cat the center location are not limited to the above-described examples,and may include various restrictions for decoding the third coding unit520 c at the center location differently from the other third codingunits 520 b and 520 d.

According to an embodiment, the image decoding apparatus 100 may obtainthe split shape mode information, which is used to split a currentcoding unit, from a preset location in the current coding unit.

FIG. 6 illustrates a method, performed by the image decoding apparatus100, of determining a preset coding unit from among an odd number ofcoding units, according to an embodiment.

Referring to FIG. 6 , split shape mode information of a current codingunit 600 or 650 may be obtained from a sample of a preset location(e.g., a sample 640 or 690 of a center location) from among a pluralityof samples included in the current coding unit 600 or 650. However, thepreset location in the current coding unit 600, from which at least onepiece of the split shape mode information may be obtained, is notlimited to the center location in FIG. 6 , and may include variouslocations included in the current coding unit 600 (e.g., top, bottom,left, right, upper left, lower left, upper right, lower right locations,or the like). The image decoding apparatus 100 may obtain the splitshape mode information from the preset location and may determine tosplit or to not split the current coding unit into various-shaped andvarious-sized coding units.

According to an embodiment, when the current coding unit is split into apreset number of coding units, the image decoding apparatus 100 mayselect one of the coding units. Various methods may be used to selectone of a plurality of coding units, as will be described below inrelation to various embodiments.

According to an embodiment, the image decoding apparatus 100 may splitthe current coding unit into a plurality of coding units, and maydetermine a coding unit at a preset location.

According to an embodiment, image decoding apparatus 100 may useinformation indicating locations of the odd number of coding units, todetermine a coding unit at a center location from among the odd numberof coding units. Referring to FIG. 6 , the image decoding apparatus 100may determine the odd number of coding units 620 a, 620 b, and 620 c orthe odd number of coding units 660 a, 660 b, and 660 c by splitting thecurrent coding unit 600 or the current coding unit 650. The imagedecoding apparatus 100 may determine the middle coding unit 620 b or themiddle coding unit 660 b by using information about the locations of theodd number of coding units 620 a, 620 b, and 620 c or the odd number ofcoding units 660 a, 660 b, and 660 c. For example, the image decodingapparatus 100 may determine the coding unit 620 b of the center locationby determining the locations of the coding units 620 a, 620 b, and 620 cbased on information indicating locations of preset samples included inthe coding units 620 a, 620 b, and 620 c. In detail, the image decodingapparatus 100 may determine the coding unit 620 b at the center locationby determining the locations of the coding units 620 a, 620 b, and 620 cbased on information indicating locations of upper-left samples 630 a,630 b, and 630 c of the coding units 620 a, 620 b, and 620 c.

According to an embodiment, the information indicating the locations ofthe upper-left samples 630 a, 630 b, and 630 c, which are included inthe coding units 620 a, 620 b, and 620 c, respectively, may includeinformation about locations or coordinates of the coding units 620 a,620 b, and 620 c in a picture. According to an embodiment, theinformation indicating the locations of the upper-left samples 630 a,630 b, and 630 c, which are included in the coding units 620 a, 620 b,and 620 c, respectively, may include information indicating widths orheights of the coding units 620 a, 620 b, and 620 c included in thecurrent coding unit 600, and the widths or heights may correspond toinformation indicating differences between the coordinates of the codingunits 620 a, 620 b, and 620 c in the picture. That is, the imagedecoding apparatus 100 may determine the coding unit 620 b at the centerlocation by directly using the information about the locations orcoordinates of the coding units 620 a, 620 b, and 620 c in the picture,or by using the information about the widths or heights of the codingunits, which correspond to the difference values between thecoordinates.

According to an embodiment, information indicating the location of theupper-left sample 630 a of the upper coding unit 620 a may includecoordinates (xa, ya), information indicating the location of theupper-left sample 630 b of the center coding unit 620 b may includecoordinates (xb, yb), and information indicating the location of theupper-left sample 630 c of the lower coding unit 620 c may includecoordinates (xc, yc). The image decoding apparatus 100 may determine themiddle coding unit 620 b by using the coordinates of the upper-leftsamples 630 a, 630 b, and 630 c which are included in the coding units620 a, 620 b, and 620 c, respectively. For example, when the coordinatesof the upper-left samples 630 a, 630 b, and 630 c are sorted in anascending or descending order, the coding unit 620 b including thecoordinates (xb, yb) of the sample 630 b at a center location may bedetermined as a coding unit at a center location from among the codingunits 620 a, 620 b, and 620 c determined by splitting the current codingunit 600. However, the coordinates indicating the locations of theupper-left samples 630 a, 630 b, and 630 c may include coordinatesindicating absolute locations in the picture, or may use coordinates(dxb, dyb) indicating a relative location of the upper-left sample 630 bof the middle coding unit 620 b and coordinates (dxc, dyc) indicating arelative location of the upper-left sample 630 c of the lower codingunit 620 c with reference to the location of the upper-left sample 630 aof the upper coding unit 620 a. A method of determining a coding unit ata preset location by using coordinates of a sample included in thecoding unit, as information indicating a location of the sample, is notlimited to the above-described method, and may include variousarithmetic methods capable of using the coordinates of the sample.

According to an embodiment, the image decoding apparatus 100 may splitthe current coding unit 600 into a plurality of coding units 620 a, 620b, and 620 c, and may select one of the coding units 620 a, 620 b, and620 c based on a preset criterion. For example, the image decodingapparatus 100 may select the coding unit 620 b, which has a sizedifferent from that of the others, from among the coding units 620 a,620 b, and 620 c.

According to an embodiment, the image decoding apparatus 100 maydetermine the width or height of each of the coding units 620 a, 620 b,and 620 c by using the coordinates (xa, ya) that is the informationindicating the location of the upper-left sample 630 a of the uppercoding unit 620 a, the coordinates (xb, yb) that is the informationindicating the location of the upper-left sample 630 b of the middlecoding unit 620 b, and the coordinates (xc, yc) that are the informationindicating the location of the upper-left sample 630 c of the lowercoding unit 620 c. The image decoding apparatus 100 may determine therespective sizes of the coding units 620 a, 620 b, and 620 c by usingthe coordinates (xa, ya), (xb, yb), and (xc, yc) indicating thelocations of the coding units 620 a, 620 b, and 620 c. According to anembodiment, the image decoding apparatus 100 may determine the width ofthe upper coding unit 620 a to be the width of the current coding unit600. The image decoding apparatus 100 may determine the height of theupper coding unit 620 a to be yb-ya. According to an embodiment, theimage decoding apparatus 100 may determine the width of the middlecoding unit 620 b to be the width of the current coding unit 600. Theimage decoding apparatus 100 may determine the height of the middlecoding unit 620 b to be yc-yb. According to an embodiment, the imagedecoding apparatus 100 may determine the width or height of the lowercoding unit 620 c by using the width or height of the current codingunit 600 or the widths or heights of the upper and middle coding units620 a and 620 b. The image decoding apparatus 100 may determine a codingunit, which has a size different from that of the others, based on thedetermined widths and heights of the coding units 620 a, 620 b, and 620c. Referring to FIG. 6 , the image decoding apparatus 100 may determinethe middle coding unit 620 b, which has a size different from the sizeof the upper and lower coding units 620 a and 620 c, as the coding unitof the preset location. However, the above-described method, performedby the image decoding apparatus 100, of determining a coding unit havinga size different from the size of the other coding units merelycorresponds to an example of determining a coding unit at a presetlocation by using the sizes of coding units, which are determined basedon coordinates of samples, and thus various methods of determining acoding unit at a preset location by comparing the sizes of coding units,which are determined based on coordinates of preset samples, may beused.

The image decoding apparatus 100 may determine the width or height ofeach of the coding units 660 a, 660 b, and 660 c by using thecoordinates (xd, yd) that are information indicating the location of anupper-left sample 670 a of the left coding unit 660 a, the coordinates(xe, ye) that are information indicating the location of an upper-leftsample 670 b of the middle coding unit 660 b, and the coordinates (xf,yf) that are information indicating a location of the upper-left sample670 c of the right coding unit 660 c. The image decoding apparatus 100may determine the respective sizes of the coding units 660 a, 660 b, and660 c by using the coordinates (xd, yd), (xe, ye), and (xf, yf)indicating the locations of the coding units 660 a, 660 b, and 660 c.

According to an embodiment, the image decoding apparatus 100 maydetermine the width of the left coding unit 660 a to be xe-xd. The imagedecoding apparatus 100 may determine the height of the left coding unit660 a to be the height of the current coding unit 650. According to anembodiment, the image decoding apparatus 100 may determine the width ofthe middle coding unit 660 b to be xf-xe. The image decoding apparatus100 may determine the height of the middle coding unit 660 b to be theheight of the current coding unit 650. According to an embodiment, theimage decoding apparatus 100 may determine the width or height of theright coding unit 660 c by using the width or height of the currentcoding unit 650 or the widths or heights of the left and middle codingunits 660 a and 660 b. The image decoding apparatus 100 may determine acoding unit, which has a size different from that of the others, basedon the determined widths and heights of the coding units 660 a, 660 b,and 660 c. Referring to FIG. 6 , the image decoding apparatus 100 maydetermine the middle coding unit 660 b, which has a size different fromthe sizes of the left and right coding units 660 a and 660 c, as thecoding unit of the preset location. However, the above-described method,performed by the image decoding apparatus 100, of determining a codingunit having a size different from the size of the other coding unitsmerely corresponds to an example of determining a coding unit at apreset location by using the sizes of coding units, which are determinedbased on coordinates of samples, and thus various methods of determininga coding unit at a preset location by comparing the sizes of codingunits, which are determined based on coordinates of preset samples, maybe used.

However, locations of samples considered to determine locations ofcoding units are not limited to the above-described upper leftlocations, and information about arbitrary locations of samples includedin the coding units may be used.

According to an embodiment, the image decoding apparatus 100 may selecta coding unit at a preset location from among an odd number of codingunits determined by splitting the current coding unit, considering theshape of the current coding unit. For example, when the current codingunit has a non-square shape, a width of which is longer than a height,the image decoding apparatus 100 may determine the coding unit at thepreset location in a horizontal direction. That is, the image decodingapparatus 100 may determine one of coding units at different locationsin a horizontal direction and may put a restriction on the coding unit.When the current coding unit has a non-square shape, a height of whichis longer than a width, the image decoding apparatus 100 may determinethe coding unit at the preset location in a vertical direction. That is,the image decoding apparatus 100 may determine one of coding units atdifferent locations in a vertical direction and may put a restriction onthe coding unit.

According to an embodiment, the image decoding apparatus 100 may useinformation indicating respective locations of an even number of codingunits, to determine the coding unit at the preset location from amongthe even number of coding units. The image decoding apparatus 100 maydetermine an even number of coding units by splitting (binary splitting)the current coding unit, and may determine the coding unit at the presetlocation by using the information about the locations of the even numberof coding units. An operation related thereto may correspond to theoperation of determining a coding unit at a preset location (e.g., acenter location) from among an odd number of coding units, which hasbeen described in detail above in relation to FIG. 6 , and thus detaileddescriptions thereof are not provided here.

According to an embodiment, when a non-square current coding unit issplit into a plurality of coding units, preset information about acoding unit at a preset location may be used in a splitting operation todetermine the coding unit at the preset location from among theplurality of coding units. For example, the image decoding apparatus 100may use at least one of block shape information and split shape modeinformation, which is stored in a sample included in a middle codingunit, in a splitting operation to determine a coding unit at a centerlocation from among the plurality of coding units determined bysplitting the current coding unit.

Referring to FIG. 6 , the image decoding apparatus 100 may split thecurrent coding unit 600 into the plurality of coding units 620 a, 620 b,and 620 c based on the split shape mode information, and may determinethe coding unit 620 b at a center location from among the plurality ofthe coding units 620 a, 620 b, and 620 c. Furthermore, the imagedecoding apparatus 100 may determine the coding unit 620 b at the centerlocation, in consideration of a location from which the split shape modeinformation is obtained. That is, the split shape mode information ofthe current coding unit 600 may be obtained from the sample 640 at acenter location of the current coding unit 600 and, when the currentcoding unit 600 is split into the plurality of coding units 620 a, 620b, and 620 c based on the split shape mode information, the coding unit620 b including the sample 640 may be determined as the coding unit atthe center location. However, information used to determine the codingunit at the center location is not limited to the split shape modeinformation, and various types of information may be used to determinethe coding unit at the center location.

According to an embodiment, preset information for identifying thecoding unit at the preset location may be obtained from a preset sampleincluded in a coding unit to be determined. Referring to FIG. 6 , theimage decoding apparatus 100 may use the split shape mode information,which is obtained from a sample at a preset location in the currentcoding unit 600 (e.g., a sample at a center location of the currentcoding unit 600) to determine a coding unit at a preset location fromamong the plurality of the coding units 620 a, 620 b, and 620 cdetermined by splitting the current coding unit 600 (e.g., a coding unitat a center location from among a plurality of split coding units). Thatis, the image decoding apparatus 100 may determine the sample at thepreset location by considering a block shape of the current coding unit600, may determine the coding unit 620 b including a sample, from whichpreset information (e.g., the split shape mode information) can beobtained, from among the plurality of coding units 620 a, 620 b, and 620c determined by splitting the current coding unit 600, and may put apreset restriction on the coding unit 620 b. Referring to FIG. 6 ,according to an embodiment, the image decoding apparatus 100 maydetermine the sample 640 at the center location of the current codingunit 600 as the sample from which the preset information may beobtained, and may put a preset restriction on the coding unit 620 bincluding the sample 640, in a decoding operation. However, the locationof the sample from which the preset information can be obtained is notlimited to the above-described location, and may include arbitrarylocations of samples included in the coding unit 620 b to be determinedfor a restriction.

According to an embodiment, the location of the sample from which thepreset information may be obtained may be determined based on the shapeof the current coding unit 600. According to an embodiment, the blockshape information may indicate whether the current coding unit has asquare or non-square shape, and the location of the sample from whichthe preset information may be obtained may be determined based on theshape. For example, the image decoding apparatus 100 may determine asample located on a boundary for splitting at least one of a width andheight of the current coding unit in half, as the sample from which thepreset information can be obtained, by using at least one of informationabout the width of the current coding unit and information about theheight of the current coding unit. As another example, when the blockshape information of the current coding unit indicates a non-squareshape, the image decoding apparatus 100 may determine one of samplesadjacent to a boundary for splitting a long side of the current codingunit in half, as the sample from which the preset information can beobtained.

According to an embodiment, when the current coding unit is split into aplurality of coding units, the image decoding apparatus 100 may use thesplit shape mode information to determine a coding unit at a presetlocation from among the plurality of coding units. According to anembodiment, the image decoding apparatus 100 may obtain the split shapemode information from a sample at a preset location in a coding unit,and may split the plurality of coding units, which are generated bysplitting the current coding unit, by using the split shape modeinformation, which is obtained from the sample of the preset location ineach of the plurality of coding units. That is, a coding unit may berecursively split based on the split shape mode information, which isobtained from the sample at the preset location in each coding unit. Anoperation of recursively splitting a coding unit has been describedabove in relation to FIG. 5 , and thus detailed descriptions thereofwill not be provided here.

According to an embodiment, the image decoding apparatus 100 maydetermine one or more coding units by splitting the current coding unit,and may determine an order of decoding the one or more coding units,based on a preset block (e.g., the current coding unit).

FIG. 7 illustrates an order of processing a plurality of coding unitswhen the image decoding apparatus 100 determines the plurality of codingunits by splitting a current coding unit, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine second coding units 710 a and 710 b by splitting a firstcoding unit 700 in a vertical direction, may determine second codingunits 730 a and 730 b by splitting the first coding unit 700 in ahorizontal direction, or may determine second coding units 750 a, 750 b,750 c, and 750 d by splitting the first coding unit 700 in vertical andhorizontal directions, based on split shape mode information.

Referring to FIG. 7 , the image decoding apparatus 100 may determine toprocess the second coding units 710 a and 710 b, which are determined bysplitting the first coding unit 700 in a vertical direction, in ahorizontal direction order 710 c. The image decoding apparatus 100 maydetermine to process the second coding units 730 a and 730 b, which aredetermined by splitting the first coding unit 700 in a horizontaldirection, in a vertical direction order 730 c. The image decodingapparatus 100 may determine the second coding units 750 a, 750 b, 750 c,and 750 d, which are determined by splitting the first coding unit 700in vertical and horizontal directions, according to a preset order(e.g., a raster scan order or Z-scan order 750 e) by which coding unitsin a row are processed and then coding units in a next row areprocessed.

According to an embodiment, the image decoding apparatus 100 mayrecursively split coding units. Referring to FIG. 7 , the image decodingapparatus 100 may determine the plurality of coding units 710 a and 710b, 730 a and 730 b, or 750 a, 750 b, 750 c, and 750 d by splitting thefirst coding unit 700, and may recursively split each of the determinedplurality of coding units 710 a, 710 b, 730 a, 730 b, 750 a, 750 b, 750c, and 750 d. A splitting method of the plurality of coding units 710 aand 710 b, 730 a and 730 b, or 750 a, 750 b, 750 c, and 750 d maycorrespond to a splitting method of the first coding unit 700.Accordingly, each of the plurality of coding units 710 a and 710 b, 730a and 730 b, or 750 a, 750 b, 750 c, and 750 d may be independentlysplit into a plurality of coding units. Referring to FIG. 7 , the imagedecoding apparatus 100 may determine the second coding units 710 a and710 b by splitting the first coding unit 700 in a vertical direction,and may determine to independently split or to not split each of thesecond coding units 710 a and 710 b.

According to an embodiment, the image decoding apparatus 100 maydetermine third coding units 720 a and 720 b by splitting the leftsecond coding unit 710 a in a horizontal direction, and may not splitthe right second coding unit 710 b.

According to an embodiment, a processing order of coding units may bedetermined based on an operation of splitting a coding unit. In otherwords, a processing order of split coding units may be determined basedon a processing order of coding units immediately before being split.The image decoding apparatus 100 may determine a processing order of thethird coding units 720 a and 720 b determined by splitting the leftsecond coding unit 710 a, independently of the right second coding unit710 b. Because the third coding units 720 a and 720 b are determined bysplitting the left second coding unit 710 a in a horizontal direction,the third coding units 720 a and 720 b may be processed in a verticaldirection order 720 c. Because the left and right second coding units710 a and 710 b are processed in the horizontal direction order 710 c,the right second coding unit 710 b may be processed after the thirdcoding units 720 a and 720 b included in the left second coding unit 710a are processed in the vertical direction order 720 c. An operation ofdetermining a processing order of coding units based on a coding unitbefore being split is not limited to the above-described example, andvarious methods may be used to independently process coding units, whichare split and determined to various shapes, in a preset order.

FIG. 8 illustrates a process, performed by the image decoding apparatus100, of determining that a current coding unit is to be split into anodd number of coding units, when the coding units are not processable ina preset order, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine that the current coding unit is to be split into an odd numberof coding units, based on obtained split shape mode information.Referring to FIG. 8 , a square first coding unit 800 may be split intonon-square second coding units 810 a and 810 b, and the second codingunits 810 a and 810 b may be independently split into third coding units820 a and 820 b, and 820 c, 820 d, and 820 e. According to anembodiment, the image decoding apparatus 100 may determine the pluralityof third coding units 820 a and 820 b by splitting the left secondcoding unit 810 a in a horizontal direction, and may split the rightsecond coding unit 810 b into the odd number of third coding units 820c, 820 d, and 820 e.

According to an embodiment, the video decoding apparatus 100 maydetermine whether any coding unit is split into an odd number of codingunits, by determining whether the third coding units 820 a and 820 b,and 820 c, 820 d, and 820 e are processable in a preset order. Referringto FIG. 8 , the image decoding apparatus 100 may determine the thirdcoding units 820 a and 820 b, and 820 c, 820 d, and 820 e by recursivelysplitting the first coding unit 800. The image decoding apparatus 100may determine whether any of the first coding unit 800, the secondcoding units 810 a and 810 b, or the third coding units 820 a and 820 b,and 820 c, 820 d, and 820 e are split into an odd number of codingunits, based on at least one of the block shape information and thesplit shape mode information. For example, a coding unit located in theright from among the second coding units 810 a and 810 b may be splitinto an odd number of third coding units 820 c, 820 d, and 820 e. Aprocessing order of a plurality of coding units included in the firstcoding unit 800 may be a preset order (e.g., a Z-scan order 830), andthe image decoding apparatus 100 may determine whether the third codingunits 820 c, 820 d, and 820 e, which are determined by splitting theright second coding unit 810 b into an odd number of coding units,satisfy a condition for processing in the preset order.

According to an embodiment, the image decoding apparatus 100 maydetermine whether the third coding units 820 a and 820 b, and 820 c, 820d, and 820 e included in the first coding unit 800 satisfy the conditionfor processing in the preset order, and the condition relates to whetherat least one of a width and height of the second coding units 810 a and810 b is to be split in half along a boundary of the third coding units820 a and 820 b, and 820 c, 820 d, and 820 e. For example, the thirdcoding units 820 a and 820 b determined when the height of the leftsecond coding unit 810 a of the non-square shape is split in half maysatisfy the condition. It may be determined that the third coding units820 c, 820 d, and 820 e do not satisfy the condition because theboundaries of the third coding units 820 c, 820 d, and 820 e determinedwhen the right second coding unit 810 b is split into three coding unitsare unable to split the width or height of the right second coding unit810 b in half. When the condition is not satisfied as described above,the image decoding apparatus 100 may determine disconnection of a scanorder, and may determine that the right second coding unit 810 b is tobe split into an odd number of coding units, based on a result of thedetermination. According to an embodiment, when a coding unit is splitinto an odd number of coding units, the image decoding apparatus 100 mayput a preset restriction on a coding unit at a preset location fromamong the split coding units. The restriction or the preset location hasbeen described above in relation to various embodiments, and thusdetailed descriptions thereof will not be provided herein.

FIG. 9 illustrates a process, performed by the image decoding apparatus100, of determining at least one coding unit by splitting a first codingunit 900, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 may splitthe first coding unit 900, based on split shape mode information, whichis obtained through the bitstream obtainer 110. The square first codingunit 900 may be split into four square coding units, or may be splitinto a plurality of non-square coding units. For example, referring toFIG. 9 , when the first coding unit 900 has a square shape and the splitshape mode information indicates to split the first coding unit 900 intonon-square coding units, the image decoding apparatus 100 may split thefirst coding unit 900 into a plurality of non-square coding units. Indetail, when the split shape mode information indicates to determine anodd number of coding units by splitting the first coding unit 900 in ahorizontal direction or a vertical direction, the image decodingapparatus 100 may split the square first coding unit 900 into an oddnumber of coding units, e.g., second coding units 910 a, 910 b, and 910c determined by splitting the square first coding unit 900 in a verticaldirection or second coding units 920 a, 920 b, and 920 c determined bysplitting the square first coding unit 900 in a horizontal direction.

According to an embodiment, the image decoding apparatus 100 maydetermine whether the second coding units 910 a, 910 b, 910 c, 920 a,920 b, and 920 c included in the first coding unit 900 satisfy acondition for processing in a preset order, and the condition relates towhether at least one of a width and height of the first coding unit 900is to be split in half along a boundary of the second coding units 910a, 910 b, 910 c, 920 a, 920 b, and 920 c. Referring to FIG. 9 , becauseboundaries of the second coding units 910 a, 910 b, and 910 c determinedby splitting the square first coding unit 900 in a vertical direction donot split the width of the first coding unit 900 in half, it may bedetermined that the first coding unit 900 does not satisfy the conditionfor processing in the preset order. Also, because boundaries of thesecond coding units 920 a, 920 b, and 920 c determined by splitting thesquare first coding unit 900 in a horizontal direction do not split theheight of the first coding unit 900 in half, it may be determined thatthe first coding unit 900 does not satisfy the condition for processingin the preset order. When the condition is not satisfied as describedabove, the image decoding apparatus 100 may decide disconnection of ascan order, and may determine that the first coding unit 900 is to besplit into an odd number of coding units, based on a result of thedecision. According to an embodiment, when a coding unit is split intoan odd number of coding units, the image decoding apparatus 100 may puta preset restriction on a coding unit at a preset location from amongthe split coding units. The restriction or the preset location has beendescribed above in relation to various embodiments, and thus detaileddescriptions thereof will not be provided herein.

According to an embodiment, the image decoding apparatus 100 maydetermine various-shaped coding units by splitting a first coding unit.

Referring to FIG. 9 , the image decoding apparatus 100 may split thesquare first coding unit 900 or a non-square first coding unit 930 or950 into various-shaped coding units.

FIG. 10 illustrates that a shape into which a second coding unit issplittable is restricted when the second coding unit having a non-squareshape, which is determined when the image decoding apparatus 100 splitsa first coding unit 1000, satisfies a preset condition, according to anembodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine to split the square first coding unit 1000 into non-squaresecond coding units 1010 a, and 1010 b or 1020 a and 1020 b, based onsplit shape mode information, which is obtained by the bitstreamobtainer 110. The second coding units 1010 a and 1010 b, or 1020 a and1020 b may be independently split. As such, the image decoding apparatus100 may determine to split or to not split each of the second codingunits 1010 a and 1010 b, or 1020 a and 1020 b into a plurality of codingunits, based on the split shape mode information of each of the secondcoding units 1010 a and 1010 b, or 1020 a and 1020 b. According to anembodiment, the image decoding apparatus 100 may determine third codingunits 1012 a and 1012 b by splitting the non-square left second codingunit 1010 a, which is determined by splitting the first coding unit 1000in a vertical direction, in a horizontal direction. However, when theleft second coding unit 1010 a is split in a horizontal direction, theimage decoding apparatus 100 may restrict the right second coding unit1010 b to not be split in a horizontal direction in which the leftsecond coding unit 1010 a is split. When third coding units 1014 a and1014 b are determined by splitting the right second coding unit 1010 bin a same direction, because the left and right second coding units 1010a and 1010 b are independently split in a horizontal direction, thethird coding units 1012 a and 1012 b, or 1014 a and 1014 b may bedetermined. However, this case serves equally as a case in which theimage decoding apparatus 100 splits the first coding unit 1000 into foursquare second coding units 1030 a, 1030 b, 1030 c, and 1030 d, based onthe split shape mode information, and may be inefficient in terms ofimage decoding.

According to an embodiment, the image decoding apparatus 100 maydetermine third coding units 1022 a and 1022 b, or 1024 a and 1024 b bysplitting the non-square second coding unit 1020 a or 1020 b, which isdetermined by splitting the first coding unit 1000 in a horizontaldirection, in a vertical direction. However, when a second coding unit(e.g., the upper second coding unit 1020 a) is split in a verticaldirection, for the above-described reason, the image decoding apparatus100 may restrict the other second coding unit (e.g., the lower secondcoding unit 1020 b) to not be split in a vertical direction in which theupper second coding unit 1020 a is split.

FIG. 11 illustrates a process, performed by the image decoding apparatus100, of splitting a square coding unit when split shape mode informationindicates that the square coding unit is to not be split into foursquare coding units, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine second coding units 1110 a and 1110 b, or 1120 a and 1120 b,etc. by splitting a first coding unit 1100, based on split shape modeinformation. The split shape mode information may include informationabout various methods of splitting a coding unit but, the informationabout various splitting methods may not include information forsplitting a coding unit into four square coding units. According to suchsplit shape mode information, the image decoding apparatus 100 may notsplit the square first coding unit 1100 into four square second codingunits 1130 a, 1130 b, 1130 c, and 1130 d. The image decoding apparatus100 may determine the non-square second coding units 1110 a and 1110 b,or 1120 a and 1120 b, etc., based on the split shape mode information.

According to an embodiment, the image decoding apparatus 100 mayindependently split the non-square second coding units 1110 a and 1110b, or 1120 a and 1120 b, etc. Each of the second coding units 1110 a and1110 b, or 1120 a and 1120 b, etc. may be recursively split in a presetorder, and this splitting method may correspond to a method of splittingthe first coding unit 1100, based on the split shape mode information.

For example, the image decoding apparatus 100 may determine square thirdcoding units 1112 a and 1112 b by splitting the left second coding unit1110 a in a horizontal direction, and may determine square third codingunits 1114 a and 1114 b by splitting the right second coding unit 1110 bin a horizontal direction. Furthermore, the image decoding apparatus 100may determine square third coding units 1116 a, 1116 b, 1116 c, and 1116d by splitting both of the left and right second coding units 1110 a and1110 b in a horizontal direction. In this case, coding units having thesame shape as the four square second coding units 1130 a, 1130 b, 1130c, and 1130 d split from the first coding unit 1100 may be determined.

As another example, the image decoding apparatus 100 may determinesquare third coding units 1122 a and 1122 b by splitting the uppersecond coding unit 1120 a in a vertical direction, and may determinesquare third coding units 1124 a and 1124 b by splitting the lowersecond coding unit 1120 b in a vertical direction. Furthermore, theimage decoding apparatus 100 may determine square third coding units1126 a, 1126 b, 1126 c, and 1126 d by splitting both the upper and lowersecond coding units 1120 a and 1120 b in a vertical direction. In thiscase, coding units having the same shape as the four square secondcoding units 1130 a, 1130 b, 1130 c, and 1130 d split from the firstcoding unit 1100 may be determined.

FIG. 12 illustrates that a processing order between a plurality ofcoding units may be changed depending on a process of splitting a codingunit, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 may split afirst coding unit 1200, based on split shape mode information. When ablock shape indicates a square shape and the split shape modeinformation indicates to split the first coding unit 1200 in at leastone of horizontal and vertical directions, the image decoding apparatus100 may determine second coding units 1210 a and 1210 b, or 1220 a and1220 b, etc. by splitting the first coding unit 1200. Referring to FIG.12 , the non-square second coding units 1210 a and 1210 b, or 1220 a and1220 b determined by splitting the first coding unit 1200 in only ahorizontal direction or vertical direction may be independently splitbased on the split shape mode information of each coding unit. Forexample, the image decoding apparatus 100 may determine third codingunits 1216 a, 1216 b, 1216 c, and 1216 d by splitting the second codingunits 1210 a and 1210 b, which are generated by splitting the firstcoding unit 1200 in a vertical direction, in a horizontal direction, andmay determine third coding units 1226 a, 1226 b, 1226 c, and 1226 d bysplitting the second coding units 1220 a and 1220 b, which are generatedby splitting the first coding unit 1200 in a horizontal direction, in avertical direction. An operation of splitting the second coding units1210 a and 1210 b, or 1220 a and 1220 b has been described above inrelation to FIG. 11 , and thus detailed descriptions thereof will not beprovided herein.

According to an embodiment, the image decoding apparatus 100 may processcoding units in a preset order. An operation of processing coding unitsin a preset order has been described above in relation to FIG. 7 , andthus detailed descriptions thereof will not be provided herein.Referring to FIG. 12 , the image decoding apparatus 100 may determinefour square third coding units 1216 a, 1216 b, 1216 c, and 1216 d, and1226 a, 1226 b, 1226 c, and 1226 d by splitting the square first codingunit 1200. According to an embodiment, the image decoding apparatus 100may determine processing orders of the third coding units 1216 a, 1216b, 1216 c, and 1216 d, and 1226 a, 1226 b, 1226 c, and 1226 d based on asplit shape by which the first coding unit 1200 is split.

According to an embodiment, the image decoding apparatus 100 maydetermine the third coding units 1216 a, 1216 b, 1216 c, and 1216 d bysplitting the second coding units 1210 a and 1210 b generated bysplitting the first coding unit 1200 in a vertical direction, in ahorizontal direction, and may process the third coding units 1216 a,1216 b, 1216 c, and 1216 d in a processing order 1217 for initiallyprocessing the third coding units 1216 a and 1216 c, which are includedin the left second coding unit 1210 a, in a vertical direction and thenprocessing the third coding unit 1216 b and 1216 d, which are includedin the right second coding unit 1210 b, in a vertical direction.

According to an embodiment, the image decoding apparatus 100 maydetermine the third coding units 1226 a, 1226 b, 1226 c, and 1226 d bysplitting the second coding units 1220 a and 1220 b generated bysplitting the first coding unit 1200 in a horizontal direction, in avertical direction, and may process the third coding units 1226 a, 1226b, 1226 c, and 1226 d in a processing order 1227 for initiallyprocessing the third coding units 1226 a and 1226 b, which are includedin the upper second coding unit 1220 a, in a horizontal direction andthen processing the third coding unit 1226 c and 1226 d, which areincluded in the lower second coding unit 1220 b, in a horizontaldirection.

Referring to FIG. 12 , the square third coding units 1216 a, 1216 b,1216 c, and 1216 d, and 1226 a, 1226 b, 1226 c, and 1226 d may bedetermined by splitting the second coding units 1210 a and 1210 b, and1220 a and 1220 b, respectively. Although the second coding units 1210 aand 1210 b are determined by splitting the first coding unit 1200 in avertical direction differently from the second coding units 1220 a and1220 b which are determined by splitting the first coding unit 1200 in ahorizontal direction, the third coding units 1216 a, 1216 b, 1216 c, and1216 d, and 1226 a, 1226 b, 1226 c, and 1226 d split therefromeventually show same-shaped coding units split from the first codingunit 1200. As such, by recursively splitting a coding unit in differentmanners based on the split shape mode information, the image decodingapparatus 100 may process a plurality of coding units in differentorders even when the coding units are eventually determined to be thesame shape.

FIG. 13 illustrates a process of determining a depth of a coding unit asa shape and a size of the coding unit change, when the coding unit isrecursively split such that a plurality of coding units are determined,according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine the depth of the coding unit, based on a preset criterion. Forexample, the preset criterion may be the length of a long side of thecoding unit. When the length of a long side of a coding unit beforebeing split is 2n times (n>0) the length of a long side of a splitcurrent coding unit, the image decoding apparatus 100 may determine thata depth of the current coding unit is increased from a depth of thecoding unit before being split, by n. In the following descriptions, acoding unit having an increased depth is expressed as a coding unit of alower depth.

Referring to FIG. 13 , according to an embodiment, the image decodingapparatus 100 may determine a second coding unit 1302 and a third codingunit 1304 of lower depths by splitting a square first coding unit 1300based on block shape information indicating a square shape (e.g., theblock shape information may be expressed as ‘0: SQUARE’). Assuming thatthe size of the square first coding unit 1300 is 2N×2N, the secondcoding unit 1302 determined by splitting a width and height of the firstcoding unit 1300 in ½ may have a size of N×N. Furthermore, the thirdcoding unit 1304 determined by splitting a width and height of thesecond coding unit 1302 in ½ may have a size of N/2×N/2. In this case, awidth and height of the third coding unit 1304 are ¼ times those of thefirst coding unit 1300. When a depth of the first coding unit 1300 is D,a depth of the second coding unit 1302, the width and height of whichare ½ times those of the first coding unit 1300, may be D+1, and a depthof the third coding unit 1304, the width and height of which are ¼ timesthose of the first coding unit 1300, may be D+2.

According to an embodiment, the image decoding apparatus 100 maydetermine a second coding unit 1312 or 1322 and a third coding unit 1314or 1324 of lower depths by splitting a non-square first coding unit 1310or 1320 based on block shape information indicating a non-square shape(e.g., the block shape information may be expressed as ‘1: NS_VER’indicating a non-square shape, a height of which is longer than a width,or as ‘2: NS_HOR’ indicating a non-square shape, a width of which islonger than a height).

The image decoding apparatus 100 may determine a second coding unit1302, 1312, or 1322 by splitting at least one of a width and height ofthe first coding unit 1310 having a size of N×2N. That is, the imagedecoding apparatus 100 may determine the second coding unit 1302 havinga size of N×N or the second coding unit 1322 having a size of N×N/2 bysplitting the first coding unit 1310 in a horizontal direction, or maydetermine the second coding unit 1312 having a size of N/2×N bysplitting the first coding unit 1310 in horizontal and verticaldirections.

According to an embodiment, the image decoding apparatus 100 maydetermine the second coding unit 1302, 1312, or 1322 by splitting atleast one of a width and height of the first coding unit 1320 having asize of 2N×N. That is, the image decoding apparatus 100 may determinethe second coding unit 1302 having a size of N×N or the second codingunit 1312 having a size of N/2×N by splitting the first coding unit 1320in a vertical direction, or may determine the second coding unit 1322having a size of N×N/2 by splitting the first coding unit 1320 inhorizontal and vertical directions.

According to an embodiment, the image decoding apparatus 100 maydetermine a third coding unit 1304, 1314, or 1324 by splitting at leastone of a width and height of the second coding unit 1302 having a sizeof N×N. That is, the image decoding apparatus 100 may determine thethird coding unit 1304 having a size of N/2×N/2, the third coding unit1314 having a size of N/4×N/2, or the third coding unit 1324 having asize of N/2×N/4 by splitting the second coding unit 1302 in vertical andhorizontal directions.

According to an embodiment, the image decoding apparatus 100 maydetermine the third coding unit 1304, 1314, or 1324 by splitting atleast one of a width and height of the second coding unit 1312 having asize of N/2×N. That is, the image decoding apparatus 100 may determinethe third coding unit 1304 having a size of N/2×N/2 or the third codingunit 1324 having a size of N/2×N/4 by splitting the second coding unit1312 in a horizontal direction, or may determine the third coding unit1314 having a size of N/4×N/2 by splitting the second coding unit 1312in vertical and horizontal directions.

According to an embodiment, the image decoding apparatus 100 maydetermine the third coding unit 1304, 1314, or 1324 by splitting atleast one of a width and height of the second coding unit 1322 having asize of N×N/2. That is, the image decoding apparatus 100 may determinethe third coding unit 1304 having a size of N/2×N/2 or the third codingunit 1314 having a size of N/4×N/2 by splitting the second coding unit1322 in a vertical direction, or may determine the third coding unit1324 having a size of N/2×N/4 by splitting the second coding unit 1322in vertical and horizontal directions.

According to an embodiment, the image decoding apparatus 100 may splitthe square coding unit 1300, 1302, or 1304 in a horizontal or verticaldirection. For example, the image decoding apparatus 100 may determinethe first coding unit 1310 having a size of N×2N by splitting the firstcoding unit 1300 having a size of 2N×2N in a vertical direction, or maydetermine the first coding unit 1320 having a size of 2N×N by splittingthe first coding unit 1300 in a horizontal direction. According to anembodiment, when a depth is determined based on the length of thelongest side of a coding unit, a depth of a coding unit determined bysplitting the first coding unit 1300 having a size of 2N×2N in ahorizontal or vertical direction may be the same as the depth of thefirst coding unit 1300.

According to an embodiment, a width and height of the third coding unit1314 or 1324 may be ¼ times those of the first coding unit 1310 or 1320.When a depth of the first coding unit 1310 or 1320 is D, a depth of thesecond coding unit 1312 or 1322, the width and height of which are ½times those of the first coding unit 1310 or 1320, may be D+1, and adepth of the third coding unit 1314 or 1324, the width and height ofwhich are ¼ times those of the first coding unit 1310 or 1320, may beD+2.

FIG. 14 illustrates depths that are determinable based on shapes andsizes of coding units, and part indexes (PIDs) that are fordistinguishing the coding units, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine various-shape second coding units by splitting a square firstcoding unit 1400. Referring to FIG. 14 , the image decoding apparatus100 may determine second coding units 1402 a and 1402 b, 1404 a and 1404b, and 1406 a, 1406 b, 1406 c, and 1406 d by splitting the first codingunit 1400 in at least one of vertical and horizontal directions based onsplit shape mode information. That is, the image decoding apparatus 100may determine the second coding units 1402 a and 1402 b, 1404 a and 1404b, and 1406 a, 1406 b, 1406 c, and 1406 d, based on the split shape modeinformation of the first coding unit 1400.

According to an embodiment, depths of the second coding units 1402 a and1402 b, 1404 a and 1404 b, and 1406 a, 1406 b, 1406 c, and 1406 d thatare determined based on the split shape mode information of the squarefirst coding unit 1400 may be determined based on the length of a longside thereof. For example, because the length of a side of the squarefirst coding unit 1400 equals the length of a long side of thenon-square second coding units 1402 a and 1402 b, and 1404 a and 1404 b,the first coding unit 1400 and the non-square second coding units 1402 aand 1402 b, and 1404 a and 1404 b may have the same depth, e.g., D.However, when the image decoding apparatus 100 splits the first codingunit 1400 into the four square second coding units 1406 a, 1406 b, 1406c, and 1406 d based on the split shape mode information, because thelength of a side of the square second coding units 1406 a, 1406 b, 1406c, and 1406 d is ½ times the length of a side of the first coding unit1400, a depth of the second coding units 1406 a, 1406 b, 1406 c, and1406 d may be D+1 which is deeper than the depth D of the first codingunit 1400 by 1.

According to an embodiment, the image decoding apparatus 100 maydetermine a plurality of second coding units 1412 a and 1412 b, and 1414a, 1414 b, and 1414 c by splitting a first coding unit 1410, a height ofwhich is longer than a width, in a horizontal direction based on thesplit shape mode information. According to an embodiment, the imagedecoding apparatus 100 may determine a plurality of second coding units1422 a and 1422 b, and 1424 a, 1424 b, and 1424 c by splitting a firstcoding unit 1420, a width of which is longer than a height, in avertical direction based on the split shape mode information.

According to an embodiment, a depth of the second coding units 1412 aand 1412 b, and 1414 a, 1414 b, and 1414 c, or 1422 a and 1422 b, and1424 a, 1424 b, and 1424 c, which are determined based on the splitshape mode information of the non-square first coding unit 1410 or 1420,may be determined based on the length of a long side thereof. Forexample, because the length of a side of the square second coding units1412 a and 1412 b is ½ times the length of a long side of the firstcoding unit 1410 having a non-square shape, a height of which is longerthan a width, a depth of the square second coding units 1412 a and 1412b is D+1 which is deeper than the depth D of the non-square first codingunit 1410 by 1.

Furthermore, the image decoding apparatus 100 may split the non-squarefirst coding unit 1410 into an odd number of second coding units 1414 a,1414 b, and 1414 c based on the split shape mode information. The oddnumber of second coding units 1414 a, 1414 b, and 1414 c may include thenon-square second coding units 1414 a and 1414 c and the square secondcoding unit 1414 b. In this case, because the length of a long side ofthe non-square second coding units 1414 a and 1414 c and the length of aside of the square second coding unit 1414 b are ½ times the length of along side of the first coding unit 1410, a depth of the second codingunits 1414 a, 1414 b, and 1414 c may be D+1 which is deeper than thedepth D of the non-square first coding unit 1410 by 1. The imagedecoding apparatus 100 may determine depths of coding units split fromthe first coding unit 1420 having a non-square shape, a width of whichis longer than a height, by using the above-described method ofdetermining depths of coding units split from the first coding unit1410.

According to an embodiment, the image decoding apparatus 100 maydetermine PIDs for identifying split coding units, based on a size ratiobetween the coding units when an odd number of split coding units do nothave equal sizes. Referring to FIG. 14 , a coding unit 1414 b of acenter location among an odd number of split coding units 1414 a, 1414b, and 1414 c may have a width equal to that of the other coding units1414 a and 1414 c and a height which is two times that of the othercoding units 1414 a and 1414 c. That is, in this case, the coding unit1414 b at the center location may include two of the other coding unit1414 a or 1414 c. Therefore, when a PID of the coding unit 1414 b at thecenter location is 1 based on a scan order, a PID of the coding unit1414 c located next to the coding unit 1414 b may be increased by 2 andthus may be 3. That is, discontinuity in PID values may be present.According to an embodiment, the image decoding apparatus 100 maydetermine whether an odd number of split coding units do not have equalsizes, based on whether discontinuity is present in PIDs for identifyingthe split coding units.

According to an embodiment, the image decoding apparatus 100 maydetermine whether to use a specific splitting method, based on PIDvalues for identifying a plurality of coding units determined bysplitting a current coding unit. Referring to FIG. 14 , the imagedecoding apparatus 100 may determine an even number of coding units 1412a and 1412 b or an odd number of coding units 1414 a, 1414 b, and 1414 cby splitting the first coding unit 1410 having a rectangular shape, aheight of which is longer than a width. The image decoding apparatus 100may use PIDs indicating respective coding units so as to identify therespective coding units. According to an embodiment, the PID may beobtained from a sample at a preset location of each coding unit (e.g.,an upper-left sample).

According to an embodiment, the image decoding apparatus 100 maydetermine a coding unit at a preset location from among the split codingunits, by using the PIDs for distinguishing the coding units. Accordingto an embodiment, when the split shape mode information of the firstcoding unit 1410 having a rectangular shape, a height of which is longerthan a width, indicates to split a coding unit into three coding units,the image decoding apparatus 100 may split the first coding unit 1410into three coding units 1414 a, 1414 b, and 1414 c. The image decodingapparatus 100 may assign a PID to each of the three coding units 1414 a,1414 b, and 1414 c. The image decoding apparatus 100 may compare PIDs ofan odd number of split coding units to determine a coding unit at acenter location from among the coding units. The image decodingapparatus 100 may determine the coding unit 1414 b having a PIDcorresponding to a middle value among the PIDs of the coding units, asthe coding unit at the center location from among the coding unitsdetermined by splitting the first coding unit 1410. According to anembodiment, the image decoding apparatus 100 may determine PIDs fordistinguishing split coding units, based on a size ratio between thecoding units when the split coding units do not have equal sizes.Referring to FIG. 14 , the coding unit 1414 b generated by splitting thefirst coding unit 1410 may have a width equal to that of the othercoding units 1414 a and 1414 c and a height which is two times that ofthe other coding units 1414 a and 1414 c. In this case, when the PID ofthe coding unit 1414 b at the center location is 1, the PID of thecoding unit 1414 c located next to the coding unit 1414 b may beincreased by 2 and thus may be 3. When the PID is not uniformlyincreased as described above, the image decoding apparatus 100 maydetermine that a coding unit is split into a plurality of coding unitsincluding a coding unit having a size different from that of the othercoding units. According to an embodiment, when the split shape modeinformation indicates to split a coding unit into an odd number ofcoding units, the image decoding apparatus 100 may split a currentcoding unit in such a manner that a coding unit of a preset locationamong an odd number of coding units (e.g., a coding unit of a centerlocation) has a size different from that of the other coding units. Inthis case, the image decoding apparatus 100 may determine the codingunit of the center location, which has a different size, by using PIDsof the coding units. However, the PIDs and the size or location of thecoding unit of the preset location are not limited to theabove-described examples, and various PIDs and various locations andsizes of coding units may be used.

According to an embodiment, the image decoding apparatus 100 may use apreset data unit where a coding unit starts to be recursively split.

FIG. 15 illustrates that a plurality of coding units are determinedbased on a plurality of preset data units included in a picture,according to an embodiment.

According to an embodiment, a preset data unit may be defined as a dataunit where a coding unit starts to be recursively split by using splitshape mode information. That is, the preset data unit may correspond toa coding unit of an uppermost depth, which is used to determine aplurality of coding units split from a current picture. In the followingdescriptions, for convenience of explanation, the preset data unit isreferred to as a reference data unit.

According to an embodiment, the reference data unit may have a presetsize and a preset shape. According to an embodiment, a reference codingunit may include M×N samples. Herein, M and N may be equal to eachother, and may be integers expressed as powers of 2. That is, thereference data unit may have a square or non-square shape, and may besplit into an integer number of coding units.

According to an embodiment, the image decoding apparatus 100 may splitthe current picture into a plurality of reference data units. Accordingto an embodiment, the image decoding apparatus 100 may split theplurality of reference data units, which are split from the currentpicture, by using the split shape mode information of each referencedata unit. The operation of splitting the reference data unit maycorrespond to a splitting operation using a quadtree structure.

According to an embodiment, the image decoding apparatus 100 maypredetermine the minimum size allowed for the reference data unitsincluded in the current picture. Accordingly, the image decodingapparatus 100 may determine various reference data units having sizesequal to or greater than the minimum size, and may determine one or morecoding units by using the split shape mode information with reference tothe determined reference data unit.

Referring to FIG. 15 , the image decoding apparatus 100 may use a squarereference coding unit 1500 or a non-square reference coding unit 1502.According to an embodiment, the shape and size of reference coding unitsmay be determined based on various data units capable of including oneor more reference coding units (e.g., sequences, pictures, slices, slicesegments, tiles, tile groups, largest coding units, or the like).

According to an embodiment, the bitstream obtainer 110 of the imagedecoding apparatus 100 may obtain, from a bitstream, at least one ofreference coding unit shape information and reference coding unit sizeinformation with respect to each of the various data units. An operationof splitting the square reference coding unit 1500 into one or morecoding units has been described above in relation to the operation ofsplitting the current coding unit 300 of FIG. 3 , and an operation ofsplitting the non-square reference coding unit 1502 into one or morecoding units has been described above in relation to the operation ofsplitting the current coding unit 400 or 450 of FIG. 4 . Thus, detaileddescriptions thereof will not be provided herein.

According to an embodiment, the image decoding apparatus 100 may use aPID for identifying the size and shape of reference coding units, todetermine the size and shape of reference coding units according to somedata units predetermined based on a preset condition. That is, thebitstream obtainer 110 may obtain, from the bitstream, only the PID foridentifying the size and shape of reference coding units with respect toeach slice, slice segment, tile, tile group, or largest coding unitwhich is a data unit satisfying a preset condition (e.g., a data unithaving a size equal to or smaller than a slice) among the various dataunits (e.g., sequences, pictures, slices, slice segments, tiles, tilegroups, largest coding units, or the like). The image decoding apparatus100 may determine the size and shape of reference data units withrespect to each data unit, which satisfies the preset condition, byusing the PID. When the reference coding unit shape information and thereference coding unit size information are obtained and used from thebitstream according to each data unit having a relatively small size,efficiency of using the bitstream may not be high, and therefore, onlythe PID may be obtained and used instead of directly obtaining thereference coding unit shape information and the reference coding unitsize information. In this case, at least one of the size and shape ofreference coding units corresponding to the PID for identifying the sizeand shape of reference coding units may be predetermined. That is, theimage decoding apparatus 100 may determine at least one of the size andshape of reference coding units included in a data unit serving as aunit for obtaining the PID, by selecting the predetermined at least oneof the size and shape of reference coding units based on the PID.

According to an embodiment, the image decoding apparatus 100 may use oneor more reference coding units included in a largest coding unit. Thatis, a largest coding unit split from a picture may include one or morereference coding units, and coding units may be determined byrecursively splitting each reference coding unit. According to anembodiment, at least one of a width and height of the largest codingunit may be integer times at least one of the width and height of thereference coding units. According to an embodiment, the size ofreference coding units may be obtained by splitting the largest codingunit n times based on a quadtree structure. That is, the image decodingapparatus 100 may determine the reference coding units by splitting thelargest coding unit n times based on a quadtree structure, and may splitthe reference coding unit based on at least one of the block shapeinformation and the split shape mode information according to variousembodiments.

FIG. 16 illustrates a processing block serving as a unit for determininga determination order of reference coding units included in a picture1600, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 maydetermine one or more processing blocks split from a picture. Theprocessing block is a data unit including one or more reference codingunits split from a picture, and the one or more reference coding unitsincluded in the processing block may be determined according to aspecific order. That is, a determination order of one or more referencecoding units determined in each processing block may correspond to oneof various types of orders for determining reference coding units, andmay vary depending on the processing block. The determination order ofreference coding units, which is determined with respect to eachprocessing block, may be one of various orders, e.g., raster scan order,Z-scan, N-scan, up-right diagonal scan, horizontal scan, and verticalscan, but is not limited to the above-mentioned scan orders.

According to an embodiment, the image decoding apparatus 100 may obtainprocessing block size information and may determine the size of one ormore processing blocks included in the picture. The image decodingapparatus 100 may obtain the processing block size information from abitstream and may determine the size of one or more processing blocksincluded in the picture. The size of processing blocks may be a presetsize of data units, which is indicated by the processing block sizeinformation.

According to an embodiment, the bitstream obtainer 110 of the imagedecoding apparatus 100 may obtain the processing block size informationfrom the bitstream according to each specific data unit. For example,the processing block size information may be obtained from the bitstreamin a data unit such as an image, sequence, picture, slice, slicesegment, tile, or tile group. That is, the bitstream obtainer 110 mayobtain the processing block size information from the bitstreamaccording to each of the various data units, and the image decodingapparatus 100 may determine the size of one or more processing blocks,which are split from the picture, by using the obtained processing blocksize information. The size of the processing blocks may be integer timesthat of the reference coding units.

According to an embodiment, the image decoding apparatus 100 maydetermine the size of processing blocks 1602 and 1612 included in thepicture 1600. For example, the image decoding apparatus 100 maydetermine the size of processing blocks based on the processing blocksize information obtained from the bitstream. Referring to FIG. 16 ,according to an embodiment, the image decoding apparatus 100 maydetermine a width of the processing blocks 1602 and 1612 to be fourtimes the width of the reference coding units, and may determine aheight of the processing blocks 1602 and 1612 to be four times theheight of the reference coding units. The image decoding apparatus 100may determine a determination order of one or more reference codingunits in one or more processing blocks.

According to an embodiment, the image decoding apparatus 100 maydetermine the processing blocks 1602 and 1612, which are included in thepicture 1600, based on the size of processing blocks, and may determinea determination order of one or more reference coding units in theprocessing blocks 1602 and 1612. According to an embodiment,determination of reference coding units may include determination of thesize of the reference coding units.

According to an embodiment, the image decoding apparatus 100 may obtain,from the bitstream, determination order information of one or morereference coding units included in one or more processing blocks, andmay determine a determination order with respect to one or morereference coding units based on the obtained determination orderinformation. The determination order information may be defined as anorder or direction for determining the reference coding units in theprocessing block. That is, the determination order of reference codingunits may be independently determined with respect to each processingblock.

According to an embodiment, the image decoding apparatus 100 may obtain,from the bitstream, the determination order information of referencecoding units according to each specific data unit. For example, thebitstream obtainer 110 may obtain the determination order information ofreference coding units from the bitstream according to each data unitsuch as an image, sequence, picture, slice, slice segment, tile, tilegroup, or processing block. Because the determination order informationof reference coding units indicates an order for determining referencecoding units in a processing block, the determination order informationmay be obtained with respect to each specific data unit including aninteger number of processing blocks.

According to an embodiment, the image decoding apparatus 100 maydetermine one or more reference coding units based on the determineddetermination order.

According to an embodiment, the bitstream obtainer 110 may obtain thedetermination order information of reference coding units from thebitstream as information related to the processing blocks 1602 and 1612,and the image decoding apparatus 100 may determine a determination orderof one or more reference coding units included in the processing blocks1602 and 1612 and determine one or more reference coding units, whichare included in the picture 1600, based on the determination order.Referring to FIG. 16 , the image decoding apparatus 100 may determinedetermination orders 1604 and 1614 of one or more reference coding unitsin the processing blocks 1602 and 1612, respectively. For example, whenthe determination order information of reference coding units isobtained with respect to each processing block, different types of thedetermination order information of reference coding units may beobtained for the processing blocks 1602 and 1612. When the determinationorder 1604 of reference coding units in the processing block 1602 is araster scan order, reference coding units included in the processingblock 1602 may be determined according to a raster scan order. Incontrast, when the determination order 1614 of reference coding units inthe other processing block 1612 is a backward raster scan order,reference coding units included in the processing block 1612 may bedetermined according to the backward raster scan order.

According to an embodiment, the image decoding apparatus 100 may decodethe determined one or more reference coding units. The image decodingapparatus 100 may decode an image, based on the reference coding unitsdetermined as described above. A method of decoding the reference codingunits may include various image decoding methods.

According to an embodiment, the image decoding apparatus 100 may obtainblock shape information indicating the shape of a current coding unit orsplit shape mode information indicating a splitting method of thecurrent coding unit, from the bitstream, and may use the obtainedinformation. The split shape mode information may be included in thebitstream related to various data units. For example, the image decodingapparatus 100 may use the split shape mode information included in asequence parameter set, a picture parameter set, a video parameter set,a slice header, a slice segment header, a tile header, or a tile groupheader. Furthermore, the image decoding apparatus 100 may obtain, fromthe bitstream, a syntax element corresponding to the block shapeinformation or the split shape mode information according to eachlargest coding unit, each reference coding unit, or each processingblock, and may use the obtained syntax element.

Hereinafter, a method of determining a split rule, according to anembodiment of the disclosure will be described in detail.

The image decoding apparatus 100 may determine a split rule of an image.The split rule may be predetermined between the image decoding apparatus100 and the image encoding apparatus 200. The image decoding apparatus100 may determine the split rule of the image, based on informationobtained from a bitstream. The image decoding apparatus 100 maydetermine the split rule based on the information obtained from at leastone of a sequence parameter set, a picture parameter set, a videoparameter set, a slice header, a slice segment header, a tile header,and a tile group header. The image decoding apparatus 100 may determinethe split rule differently according to frames, slices, tiles, temporallayers, largest coding units, or coding units.

The image decoding apparatus 100 may determine the split rule based on ablock shape of a coding unit. The block shape may include a size, shape,a ratio of width and height, and a direction of the coding unit. Theimage encoding apparatus 200 and the image decoding apparatus 100 maypredetermine to determine the split rule based on the block shape of thecoding unit. However, the embodiment is not limited thereto. The imagedecoding apparatus 100 may determine the split rule based on theinformation obtained from the bitstream received from the image encodingapparatus 200.

The shape of the coding unit may include a square and a non-square. Whenthe lengths of the width and height of the coding unit are the same, theimage decoding apparatus 100 may determine the shape of the coding unitto be a square. Also, when the lengths of the width and height of thecoding unit are not the same, the image decoding apparatus 100 maydetermine the shape of the coding unit to be a non-square.

The size of the coding unit may include various sizes, such as 4×4, 8×4,4×8, 8×8, 16×4, 16×8, and to 256×256. The size of the coding unit may beclassified based on the length of a long side of the coding unit, thelength of a short side, or the area. The image decoding apparatus 100may apply the same split rule to coding units classified as the samegroup. For example, the image decoding apparatus 100 may classify codingunits having the same lengths of the long sides as having the same size.Also, the image decoding apparatus 100 may apply the same split rule tocoding units having the same lengths of long sides.

The ratio of the width and height of the coding unit may include 1:2,2:1, 1:4, 4:1, 1:8, 8:1, 1:16, 16:1, 32:1, 1:32, or the like. Also, adirection of the coding unit may include a horizontal direction and avertical direction. The horizontal direction may indicate a case inwhich the length of the width of the coding unit is longer than thelength of the height thereof. The vertical direction may indicate a casein which the length of the width of the coding unit is shorter than thelength of the height thereof.

The image decoding apparatus 100 may adaptively determine the split rulebased on the size of the coding unit. The image decoding apparatus 100may differently determine an allowable split shape mode based on thesize of the coding unit. For example, the image decoding apparatus 100may determine whether splitting is allowed based on the size of thecoding unit. The image decoding apparatus 100 may determine a splitdirection according to the size of the coding unit. The image decodingapparatus 100 may determine an allowable split type according to thesize of the coding unit.

The split rule determined based on the size of the coding unit may be asplit rule predetermined between the image encoding apparatus 200 andthe image decoding apparatus 100. Also, the image decoding apparatus 100may determine the split rule based on the information obtained from thebitstream.

The image decoding apparatus 100 may adaptively determine the split rulebased on a location of the coding unit. The image decoding apparatus 100may adaptively determine the split rule based on the location of thecoding unit in the image.

Also, the image decoding apparatus 100 may determine the split rule suchthat coding units generated via different splitting paths do not havethe same block shape. However, an embodiment is not limited thereto, andthe coding units generated via different splitting paths have the sameblock shape. The coding units generated via the different splittingpaths may have different decoding processing orders. Because thedecoding processing orders is described above with reference to FIG. 12, details thereof are not provided again.

FIG. 17 illustrates coding units that are determinable for each ofpictures when a split shape combination for a coding unit varies foreach picture, according to an embodiment.

Referring to FIG. 17 , the image decoding apparatus 100 may determine asplit shape combination for a coding unit to differ in each picture. Forexample, the image decoding apparatus 100 may decode an image by using apicture 1700 that is splittble into four coding units, a picture 1710that is splittble into two or four coding units, and a picture 1720 thatis splittble into two, three, or four coding units, from among one ormore pictures included in the image. To split the picture 1700 into aplurality of coding units, the image decoding apparatus 100 may use onlysplit shape information indicating splitting into four square codingunits. To split the picture 1710, the image decoding apparatus 100 mayuse only split shape information indicating splitting into two or fourcoding units. To split the picture 1720, the image decoding apparatus100 may use only split shape information indicating splitting into two,three, or four coding units. The above-described split shapecombinations are embodiments for describing operations of the imagedecoding apparatus 100, and therefore, the above-described split shapecombinations should not be interpreted to be limited to theabove-described embodiments. It should be interpreted that various splitshape combinations can be used for each preset data unit.

According to an embodiment, the bitstream obtainer 110 of the imagedecoding apparatus 100 may obtain a bitstream including an indexrepresenting a combination of split shape information for each presetdata unit (for example, a sequence, a picture, a slice, a slice segment,a tile, a tile group, etc.). For example, the bitstream obtainer 110 mayobtain an index representing a combination of split shape informationfrom a sequence parameter set, a picture parameter set, a slice header,a tile header, or a tile group header. The image decoding apparatus 100may use the obtained index to determine, for each preset data unit, asplit shape combination into which coding units can be split, and thus,may use different split shape combinations for each preset data unit.

FIG. 18 illustrates various shapes of a coding unit which may bedetermined based on split shape mode information that can be representedas a binary code, according to an embodiment.

According to an embodiment, the image decoding apparatus 100 may split acoding unit into various shapes by using block shape information andsplit shape mode information obtained by the bitstream obtainer 110.Shapes into which a coding unit can be split may correspond to variousshapes including shapes described above through the embodiments.

Referring to FIG. 18 , the image decoding apparatus 100 may split asquare coding unit in at least one direction of a horizontal directionand a vertical direction, and a non-square coding unit in the horizontaldirection or the vertical direction, based on split shape modeinformation.

According to an embodiment, when the image decoding apparatus 100 canobtain four square coding units by splitting the square coding unit inthe horizontal direction and the vertical direction, four split shapesmay be indicated by the split shape mode information for the squarecoding unit. According to an embodiment, the split shape modeinformation may be represented as a binary code of 2 digits, and abinary code may be allocated to each of split shapes. For example, whena coding unit is not split, split shape mode information may berepresented as (00)b, when a coding unit is split in the horizontaldirection and the vertical direction, split shape mode information maybe represented as (01)b, when a coding unit is split in the horizontaldirection, split shape mode information may represented as (10)b, andwhen a coding unit is split in the vertical direction, split shape modeinformation may be represented as (11)b.

According to an embodiment, types of split shapes that can be indicatedby split shape mode information when the image decoding apparatus 100splits a non-square coding unit in the horizontal direction or thevertical direction may be determined according to the number of codingunits into which the coding unit is to be split. Referring to FIG. 18 ,the image decoding apparatus 100 may split the non-square coding unit upto three coding units, according to an embodiment. Also, the imagedecoding apparatus 100 may split a coding unit into two coding units,and in this case, split shape mode information may be represented as(10)b. The image decoding apparatus 100 may split a coding unit intothree coding units, and in this case, split shape mode information maybe represented as (11)b. The image decoding apparatus 100 may determineto not split a coding unit, and in this case, split shape modeinformation may be represented as (0)b. That is, the image decodingapparatus 100 may use variable length coding (VLC), instead of fixedlength coding (FLC), so as to use a binary code representing split shapemode information.

According to an embodiment, referring to FIG. 18 , a binary code ofsplit shape mode information indicating that a coding unit is to not besplit may be represented as (0)b. In a case where a binary code of splitshape mode information indicating that a coding unit is to not be splitis set to (00)b, even when split shape mode information set to (01)bdoes not exist, a binary code of 2-bits split shape mode information hasto be all used. However, as illustrated in FIG. 18 , in a case wherethree split shapes are used for a non-square coding unit, the imagedecoding apparatus 100 can determine that a coding unit is to not besplit, by using a binary code (0)b of 1 bit as split shape modeinformation, thereby efficiently using a bitstream. However, splitshapes of a non-square coding unit, which are indicated by split shapemode information, should be not interpreted to be limited to threeshapes illustrated in FIG. 18 , and should be interpreted to be variousshapes including the above-described embodiments.

FIG. 19 illustrates other shapes of a coding unit which may bedetermined based on split shape mode information that can be representedas a binary code, according to an embodiment.

Referring to FIG. 19 , the image decoding apparatus 100 may split asquare coding unit in the horizontal direction or the verticaldirection, and a non-square coding unit in the horizontal direction orthe vertical direction, based on the split shape mode information. Thatis, the split shape mode information may indicate splitting the squarecoding unit in one direction. In this case, a binary code of split shapemode information indicating that a square coding unit is to not be splitmay be represented as (0)b. In a case where a binary code of split shapemode information indicating that a coding unit is to not be split is setto (00)b, even when split shape mode information set to (01)b does notexist, a binary code of 2-bits split shape mode information has to beall used. However, as illustrated in FIG. 19 , in a case where threesplit shapes are used for a square coding unit, the image decodingapparatus 100 can determine that a coding unit is to not be split, byusing a binary code (0)b of 1 bit as split shape mode information,thereby efficiently using a bitstream. However, split shapes of a squarecoding unit, which are indicated by split shape mode information, shouldbe not interpreted to be limited to three shapes illustrated in FIG. 19, and should be interpreted to be various shapes including theabove-described embodiments.

According to an embodiment, block shape information or split shape modeinformation may be represented using a binary code, and such informationmay be generated directly as a bitstream. Also, the block shapeinformation or the split shape mode information that may be representedusing a binary code may not be generated directly as a bitstream but maybe used as an input binary code in context adaptive binary arithmeticcoding (CABAC).

A process in which the image decoding apparatus 100 obtains a syntax forblock shape information or split shape mode information through CABAC,according to an embodiment, will be described. The image decodingapparatus 100 may obtain a bitstream including a binary code for thesyntax through the bitstream obtainer 110. The image decoding apparatus100 may detect a syntax element indicating the block shape informationor the split shape mode information by de-binarizing a bin stringincluded in the obtained bitstream. According to an embodiment, theimage decoding apparatus 100 may obtain a group of binary bin stringscorresponding to a syntax element to be decoded, and may decode each ofbins by using probability information. The image decoding apparatus 100may repeat the operation until a bin string configured with the decodedbins is identical to one of previously obtained bin strings. The imagedecoding apparatus 100 may determine the syntax element by performingde-binarization on the bin string.

According to an embodiment, the image decoding apparatus 100 may performa decoding process of adaptive binary arithmetic coding to determine asyntax for the bin string, and may update a probability model for thebins obtained through the bitstream obtainer 110. Referring to FIG. 18 ,the bitstream obtainer 110 of the image decoding apparatus 100 mayobtain a bitstream indicating a binary code representing split shapemode information, according to an embodiment. The image decodingapparatus 100 may determine a syntax for the split shape modeinformation by using the obtained binary code having a size of 1 bit or2 bits. To determine the syntax for the split shape mode information,the image decoding apparatus 100 may update a probability for each bitof the binary code of 2 bits. That is, the image decoding apparatus 100may update, according to which one of 0 or 1 a value of a first bin ofthe binary code of 2 bits is, a probability that a next bin will have avalue of 0 or 1 in decoding.

According to an embodiment, in the process of determining the syntax,the image decoding apparatus 100 may update probabilities for the binsthat are used in a process of decoding the bins of the bin string forthe syntax. In this regard, the image decoding apparatus 100 may notupdate a probability of a specific bit of the bin string and maydetermine that the specific bit has a same probability.

Referring to FIG. 18 , in a process of determining a syntax by using abin string representing split shape mode information for a non-squarecoding unit, the image decoding apparatus 100 may determine a syntax forthe split shape mode information by using a bin having a value of 0 whenthe non-square coding unit is not split. That is, when block shapeinformation indicates that a current coding unit has a non-square shape,a first bin of the bin string for the split shape mode information maybe 0 when the non-square coding unit is to not be split, and may be 1when the non-square coding unit is to be split into two or three codingunits. Accordingly, a probability that the first bin of the bin stringof the split shape mode information for the non-square coding unit willbe 0 may be ⅓, and a probability that the first bin will be 1 may be ⅔.As described above, split shape mode information indicating that anon-square coding unit is to not be split may be represented as only abin string of 1 bit having a value of 0, such that the image decodingapparatus 100 may determine the syntax for the split shape modeinformation by determining, only when the first bin of the split shapemode information is 1, whether a second bin is 0 or 1. According to anembodiment, when the first bin of the split shape mode information is 1,the image decoding apparatus 100 may determine that a probability thatthe second bin will be 0 is equal to a probability that the second binwill be 1, and may decode a next bin.

Accordingly, in the process of determining the bins of the bin stringfor the split shape mode information, the image decoding apparatus 100may use various probabilities for each of the bins. According to anembodiment, the image decoding apparatus 100 may determine a probabilityof a bin for split shape mode information to differ according to adirection of a non-square block. According to an embodiment, the imagedecoding apparatus 100 may determine a probability of a bin for splitshape mode information to differ according to a width of a currentcoding unit or a length of a longer side of the current coding unit.According to an embodiment, the image decoding apparatus 100 maydetermine a probability of a bin for split shape mode information todiffer according to at least one of a shape of a current coding unit anda length of a longer side of the current coding unit.

According to an embodiment, the image decoding apparatus 100 maydetermine that a probability of a bin for split shape mode informationto be the same with respect to coding units that are equal to or greaterthan a preset size. For example, the image decoding apparatus 100 maydetermine that a probability of a bin for split shape mode informationto be the same with respect to coding units of which lengths of longersides are equal to or greater than 64 samples.

According to an embodiment, the image decoding apparatus 100 maydetermine initial probabilities for bins constituting a bin string ofsplit shape mode information, based on a slice type (for example, an Islice, a P slice, or a B slice).

FIG. 20 is a block diagram of an image encoding and decoding system thatperforms loop filtering.

An encoder 2010 of an image encoding and decoding system 2000 maytransmit an encoded bitstream of an image, and a decoder 2050 may outputa reconstructed image by receiving and decoding the bitstream. In thisregard, the encoder 2010 may be a configuration that is similar to theimage encoding apparatus 200 to be described below, and the decoder 2050may be a configuration that is similar to the image decoding apparatus100.

In the encoder 2010, a prediction encoder 2015 may output predictiondata through inter prediction and intra prediction, and a transformerand quantizer 2020 may output a quantized transform coefficient ofresidual data between the prediction data and a current input image. Anentropy encoder 2025 may transform the quantized transform coefficientby encoding the quantized transform coefficient, and may output thequantized transform coefficient as a bitstream. The quantized transformcoefficient may be reconstructed as spatial-domain data through aninverse-quantizer and inverse-transformer 2030, and the reconstructedspatial-domain data may be output as a reconstructed image through adeblocking filter 2035 and a loop filter 2040. The reconstructed imagemay be used as a reference image of a next input image by a predictionencoder 2015.

Encoded image data of a bitstream received by the decoder 2050 may bereconstructed as spatial-domain residual data through an entropy decoder2055 and an inverse-quantizer and inverse-transformer 2060. Predictiondata output from a prediction decoder 2075 may be combined with theresidual data to construct spatial-domain image data, and a deblockingfilter 2065 and a loop filter 2070 may perform filtering on thespatial-domain image data and may output a reconstructed image for acurrent original image. The reconstructed image may be used as areference image for a next original image by the prediction decoder2075.

The loop filter 2040 of the encoder 2010 may perform loop filtering byusing filter information input according to a user input or a systemsetting. The filter information used by the loop filter 2040 may beoutput to the entropy encoder 2025, and may be transmitted to thedecoder 2050 together with encoded image data. The loop filter 2070 ofthe decoder 2050 may perform loop filtering based on filter informationinput from the decoder 2050.

Various embodiments described above describe operations related to animage decoding method that is performed by the image decoder 100.Hereinafter, operations of the image encoding apparatus 200 thatperforms an image encoding method corresponding to a reverse order ofthe image decoding method will be described through various embodiments.

FIG. 2 is a block diagram of the image encoding apparatus 200 capable ofencoding an image based on at least one of block shape information andsplit shape mode information, according to an embodiment.

The image encoding apparatus 200 may include an encoder 220 and abitstream generator 210. The encoder 220 may receive an input image andencode the input image.

The encoder 220 may obtain at least one syntax element by encoding theinput image. The syntax element may include at least one of a skip flag,a prediction mode, a motion vector difference, a motion vectorprediction method (or index), a transform quantized coefficient, a codedblock pattern, a coded block flag, an intra prediction mode, a directflag, a merge flag, a delta QP, a reference index, a predictiondirection, and a transform index. The encoder 220 may determine acontext model based on block shape information including at least one ofa shape, a direction, a ratio of a height and a width, or a size of acoding unit.

The bitstream generator 210 may generate a bitstream based on theencoded input image. For example, the bitstream generator 210 maygenerate a bitstream by entropy encoding a syntax element, based on thecontext model. Also, the image encoding apparatus 200 may transmit thebitstream to the image decoding apparatus 100.

According to an embodiment, the encoder 220 of the image encodingapparatus 200 may determine a shape of a coding unit. For example, thecoding unit may have a square shape or a non-square shape, andinformation indicating such a shape may be included in the block shapeinformation.

According to an embodiment, the encoder 220 may determine a shape intowhich the coding unit is to be split. The encoder 220 may determine ashape of at least one coding unit included in a coding unit, and thebitstream generator 210 may generate a bitstream including split shapemode information including information about the shape of the codingunit.

According to an embodiment, the encoder 220 may determine whether acoding unit is to be split or is to not be split. When the encoder 220determines that a coding unit includes only one coding unit or that acoding unit is not split, the bitstream generator 210 may generate abitstream including split shape mode information representing that thecoding unit is not split. Also, the encoder 220 may split a coding unitinto a plurality of coding units included in the coding unit, and thebitstream generator 210 may generate a bitstream including split shapemode information indicating that the coding unit is to be split into theplurality of coding units.

According to an embodiment, information representing the number ofcoding units into which a coding unit is split or a direction in whichthe coding unit is split may be included in the split shape modeinformation. For example, the split shape mode information may indicatesplitting in at least one direction of a vertical direction and ahorizontal direction or may indicate non-splitting.

The image encoding apparatus 200 may determine split shape modeinformation based on a split shape mode of a coding unit. The imageencoding apparatus 200 may determine a context model based on at leastone of a shape, a direction, a ratio of a width and a height, or a sizeof the coding unit. Also, the image encoding apparatus 200 may generate,as a bitstream, information about a split shape mode for splitting thecoding unit based on the context model.

To determine the context model, the image encoding apparatus 200 mayobtain an arrangement for matching at least one of a shape, a direction,a ratio of a width and a height, or a size of the coding unit to anindex for the context model. The image encoding apparatus 200 may obtainthe index for the context model based on at least one of the shape, thedirection, the ratio of the width and the height, or the size of thecoding unit, from the arrangement. The image encoding apparatus 200 maydetermine the context model based on the index for the context model.

To determine the context model, the image encoding apparatus 200 maydetermine the context model further based on block shape informationincluding at least one of a shape, a direction, a ratio of a width and aheight, or a size of a neighboring coding unit adjacent to the codingunit. Also, the neighboring coding unit may include at least one ofcoding units located to the lower-left side, left side, upper-left side,upper side, upper-right side, right side, or lower-right side of thecoding unit.

Also, to determine the context model, the image encoding apparatus 200may compare a length of a width of the upper neighboring coding unitwith a length of the width of the coding unit. Also, the image encodingapparatus 200 may compare lengths of heights of the left and rightneighboring coding units with a length of the height of the coding unit.Also, the image encoding apparatus 200 may determine the context modelbased on results of the comparisons.

Operations of the image encoding apparatus 200 include contents that aresimilar to those of the image decoding apparatus 100 described abovewith reference to FIGS. 3 to 20 , and thus, detailed descriptionsthereof are not provided.

Hereinafter, an image encoding apparatus 2900 and an image decodingapparatus 2100 for encoding and decoding an image in a triangleprediction mode will now be described with reference to FIGS. 21 to 30 .

FIG. 21 is a block diagram illustrating a configuration of the imagedecoding apparatus 2100 according to an embodiment.

Referring to FIG. 21 , the image decoding apparatus 2100 according to anembodiment may include an entropy decoder 2110 and a prediction decoder2130.

The entropy decoder 2110 and the prediction decoder 2130 may correspondto the decoder 120 shown in FIG. 1 . Also, the entropy decoder 2110 andthe prediction decoder 2130 may respectively correspond to the entropydecoder 2055 and the prediction decoder 2075 shown in FIG. 20 . Althoughnot illustrated in FIG. 21 , the image decoding apparatus 2100 accordingto an embodiment may further include a bitstream obtainer for obtaininga bitstream generated as a result of image encoding.

The entropy decoder 2110 and the prediction decoder 2130 according to anembodiment may be implemented as at least one processor. The imagedecoding apparatus 2100 may include one or more memories (not shown) forstoring input and output data of the entropy decoder 2110 and theprediction decoder 2130. Also, the image decoding apparatus 2100 mayinclude a memory controller (not shown) for controlling data inputs andoutputs of the memory (not shown).

The entropy decoder 2110 entropy decodes binary values included in thebitstream, thereby obtaining values corresponding to syntax elements.The entropy decoder 2110 may decode the bitstream through CABAC.

The bitstream may include a plurality of pieces of information to beused in reconstruction of a current block. The current block may be ablock generated by being split from an image according to a treestructure, and may correspond to a block such as a largest coding unit,a coding unit, or a transform unit, etc.

The prediction decoder 2130 may determine the current block based onblock shape information and/or split shape mode information included inthe bitstream corresponding to at least one level among a sequenceparameter set, a picture parameter set, a video parameter set, a sliceheader, and a slice segment header.

The bitstream may include information indicating a prediction mode ofthe current block. The prediction mode of the current block may includean intra mode, an inter mode, etc. The inter mode may be a mode forpredicting and reconstructing a current block based on a reference imageso as to reduce temporal redundancy between images. The inter mode mayinclude a regular merge mode, a merge mode using a differential motionvector, a triangle prediction mode, or the like which will be describedbelow.

When a prediction mode of the current block is determined, theprediction decoder 2130 reconstructs the current block according to thedetermined prediction mode. The reconstructed block may serve as areference block of a block to be decoded thereafter.

In an image decoding method according to an embodiment, the currentblock may be reconstructed according to the triangle prediction mode.The triangle prediction mode refers to a mode in which a current blockis split into two triangular partitions, prediction blocks correspondingto the split two triangular partitions are combined according to a splitshape so as to generate a final prediction block, and the current blockis reconstructed based on the final prediction block. For example, theprediction decoder 2130 may determine the final prediction block as areconstructed block. As another example, a result obtained by combiningthe final prediction block and residual data obtained from a bitstreammay be determined as the reconstructed block.

When the triangle prediction mode is applied to the current block, thecurrent block having a square shape has to be split into two triangularpartitions, and due to the restrictions, it may be disadvantageous toapply the triangle prediction mode to the current block, in terms of abitrate. In other words, information related to a triangle predictionmode has to be obtained from a bitstream so as to reconstruct thecurrent block according to the final prediction block, however, even ina situation where the final prediction block is to not be applied, theinformation related to a triangle prediction mode is included in thebitstream such that the number of unnecessary bits may be increased.

Accordingly, in an embodiment, the entropy decoder 2110 may determine,based on a preset condition, whether to obtain the information relatedto a triangle prediction mode from the bitstream, and only when thepreset condition is satisfied, the entropy decoder 2110 may entropydecode the information related to a triangle prediction mode from thebitstream. In contrast, when the preset condition is not satisfied, theentropy decoder 2110 may not perform entropy decoding on the informationrelated to a triangle prediction mode. The image encoding apparatus 2900may also determine, based on the preset condition, whether to apply thetriangle prediction mode to the current block, and thus, when the presetcondition is not satisfied, the image encoding apparatus 2900 may notadd the information related to the triangle prediction mode to thebitstream.

The information related to a triangle prediction mode the entropydecoder 2110 obtains from the bitstream may include informationindicating whether to apply the triangle prediction mode, split shapeinformation, and information indicating a motion vector for triangularpartitions. In an embodiment, the entropy decoder 2110 may determinethat the triangle prediction mode is to be applied to the current blockwhen the preset condition is satisfied, and may obtain, as theinformation related to a triangle prediction mode, the split shapeinformation and the information indicating a motion vector fortriangular partitions from the bitstream.

In a first embodiment, the entropy decoder 2110 may compare a size ofthe current block with a first threshold value, and when a result of thecomparison satisfies the preset condition, the entropy decoder 2110 mayobtain the information related to a triangle prediction mode for thecurrent block from a bitstream. For example, when a height of thecurrent block is smaller than the first threshold value and a width ofthe current block is smaller than the first threshold value, the entropydecoder 2110 may obtain the information related to a triangle predictionmode from the bitstream. In contrast, when a height or a width of thecurrent block is equal to or greater than the first threshold value, theentropy decoder 2110 may not obtain the information related to atriangle prediction mode from the bitstream. Also, for example, when aheight or a width of the current block is smaller than the firstthreshold value, the entropy decoder 2110 may obtain the informationrelated to a triangle prediction mode from the bitstream. In contrast,when both a height and a width of the current block are equal to orgreater than the first threshold value, the entropy decoder 2110 may notobtain the information related to a triangle prediction mode from thebitstream.

The first embodiment is provided to restrict that the triangleprediction mode is to be applied to a large-size current block. Becausesizes of two triangular partitions obtained from the large-size currentblock are large, sameness between a final prediction block and thecurrent block may be decreased, compared to a case where the currentblock is quad split or ternary split. Accordingly, in the firstembodiment, it is determined that the triangle prediction mode is to notbe applied to the current block when the size of the current block isequal to or greater than the first threshold value, and the informationrelated to a triangle prediction mode may not be parsed from thebitstream.

In a second embodiment, the entropy decoder 2110 may compare a size ofthe current block with a second threshold value, and when a result ofthe comparison satisfies the preset condition, the entropy decoder 2110may obtain the information related to a triangle prediction mode for thecurrent block from a bitstream. For example, when a value obtained bymultiplying a height of a current block by a width of the current blockis equal to or greater than the second threshold value, the entropydecoder 2110 may obtain the information related to a triangle predictionmode from the bitstream. In contrast, when a value obtained bymultiplying a height of the current block by a width of the currentblock is smaller than the second threshold value, the entropy decoder2110 may not obtain the information related to a triangle predictionmode from the bitstream. Also, for example, when both a height and awidth of the current block are equal to or greater than the secondthreshold value, the entropy decoder 2110 may obtain the informationrelated to a triangle prediction mode from the bitstream. In contrast,when a height or a width of the current block is smaller than the secondthreshold value, the entropy decoder 2110 may not obtain the informationrelated to a triangle prediction mode from the bitstream.

The second threshold value may be smaller than the first threshold valuedescribed with reference to the first embodiment. For example, the firstthreshold value may be 128, and the second threshold value may be 64. Inanother embodiment, the second threshold value and the first thresholdvalue may be identical. For example, both the first threshold value andthe second threshold value may be 64.

The second embodiment is provided to restrict that the triangleprediction mode is to be applied to a small-size current block. When acurrent block of a very small size is split into two triangularpartitions, complexity of an encoding and decoding process is large,compared to its coding efficiency. Accordingly, in the secondembodiment, when a size of the current block is smaller than the secondthreshold value, it may be determined that the triangle prediction modeis to not be applied to the current block, and information related to atriangle prediction mode may not be parsed from the bitstream.

In a third embodiment, when a prediction mode of a current block is notan inter-intra combination mode, the entropy decoder 2110 may obtaininformation related to a triangle prediction mode from a bitstream. Incontrast, when a prediction mode of the current block is the inter-intracombination mode, the entropy decoder 2110 may not obtain informationrelated to a triangle prediction mode from the bitstream.

The inter-intra combination mode refers to a mode in which a predictionblock in a reference image, the prediction block being indicated by amotion vector of the current block, is combined with a prediction blockobtained from pixels in a current image such that the current block isreconstructed. That is, a current block is reconstructed by combining aprediction block obtained according to an inter mode with a predictionblock obtained according to an intra mode.

In a conventional case where a current block is encoded without beingsplit or the current block is split and then encoded, according to aninter mode, when a cost (e.g., a rate-distortion cost) is high, theinter-intra combination mode may be applied as a prediction mode of thecurrent block. That is, the fact that the inter-intra combination modeis applied to the current block may indicate that a coding efficiency isnot good even when the current block is partitioned, such that, when theprediction mode of the current block is the inter-intra combinationmode, the entropy decoder 2110 does not obtain, from the bitstream, theinformation related to a triangle prediction mode that requirespartitioning of the current block.

In a fourth embodiment, when the prediction mode of the current block isthe merge mode using a differential motion vector, the entropy decoder2110 may not obtain information related to a triangle prediction modefrom a bitstream. In contrast, when the prediction mode of the currentblock is not the merge mode using a differential motion vector, theentropy decoder 2110 may obtain the information related to a triangleprediction mode from the bitstream.

To first describe the merge mode, the merge mode refers to a mode inwhich a merge list including motion vectors of pre-encoded orpre-decoded blocks is generated to determine a motion vector of acurrent block, and then one of the motion vectors included in the mergelist is determined to be the motion vector of the current block. Theimage encoding apparatus 2900 may transmit, to the image decodingapparatus 2100, only an index indicating a motion vector to be used asthe motion vector of the current block from among the motion vectorsincluded in the merge list, and the image decoding apparatus 2100 mayreconstruct the motion vector of the current block according to thereceived index. That is, encoding of the motion vector is enabled onlywith the index, such that efficiency may be increased, in terms of abitrate. The image decoding apparatus 2100 may obtain the motion vectorof the current block according to the index received from the imageencoding apparatus 2900, and may determine a reconstructed block, basedon a prediction block indicated by the obtained motion vector.

As in the merge mode, a merge mode using a differential motion vectordetermines one of the motion vectors included in the merge list to bethe motion vector of the current block but is different in that adifferential motion vector between an actual motion vector of thecurrent block and the motion vector selected from the merge list issignaled to the image decoding apparatus 2100. The differential motionvector may be represented as a variation distance and a variationdirection. That is, the image encoding apparatus 2900 may transmitinformation indicating the variation distance and the variationdirection corresponding to the differential motion vector, and an indexindicating one of the motion vectors included in the merge list to theimage decoding apparatus 2100, and the image decoding apparatus 2100 mayselect a motion vector indicated by the index from among the motionvectors included in the merge list, may change the selected motionvector according to the variation distance and the variation direction,and thus, may determine a motion vector of the current block.

The fact that the merge mode using a differential motion vector isapplied to a current block indicates that efficiency is good when thecurrent block is encoded/decoded by using a motion vector included inthe merge list without a need to partition the current block.Accordingly, when the merge mode using a differential motion vector isapplied to a current block, the entropy decoder 2110 may not obtaininformation related to a triangle prediction mode from a bitstream.

The entropy decoder 2110 may combine conditions described above withreference to the first embodiment, the second embodiment, the thirdembodiment, and the fourth embodiment so as to determine whether toobtain the information related to a triangle prediction mode from thebitstream.

For example, when the result of the comparison between the size of thecurrent block and the first threshold value, and the result of thecomparison between the size of the current block and the secondthreshold value satisfy the preset condition, the entropy decoder 2110may obtain the information related to a triangle prediction mode fromthe bitstream. For example, when the height and the width of the currentblock are smaller than the first threshold value, and a result obtainedby multiplying the height of the current block by the width of thecurrent block is equal to or greater than the second threshold value,the entropy decoder 2110 may obtain the information related to atriangle prediction mode from the bitstream.

As another example, the entropy decoder 2110 may obtain the informationrelated to a triangle prediction mode from the bitstream, according tothe result of the comparison between the size of the current block andthe first threshold value, and whether the prediction mode of thecurrent block is the inter-intra combination mode. For example, when theheight and the width of the current block are smaller than the firstthreshold value, and the prediction mode of the current block is not theinter-intra combination mode, the entropy decoder 2110 may obtain theinformation related to a triangle prediction mode from the bitstream.

As another example, the entropy decoder 2110 may obtain the informationrelated to a triangle prediction mode from the bitstream, according tothe result of the comparison between the size of the current block andthe first threshold value, and whether the prediction mode of thecurrent block is the merge mode using a differential motion vector. Forexample, when the height or the width of the current block is equal toor greater than the first threshold value, or the prediction mode of thecurrent block is the merge mode using a differential motion vector, theentropy decoder 2110 may not obtain the information related to atriangle prediction mode from the bitstream.

As another example, the entropy decoder 2110 may obtain the informationrelated to a triangle prediction mode from the bitstream, according tothe result of the comparison between the size of the current block andthe first threshold value, the result of the comparison between the sizeof the current block and the second threshold value, and whether theprediction mode of the current block is the inter-intra combinationmode. For example, when the height and the width of the current blockare smaller than the first threshold value, the value obtained bymultiplying the height of the current block by the width of the currentblock is equal to or greater than the second threshold value, and theprediction mode of the current block is not the inter-intra combinationmode, the entropy decoder 2110 may obtain the information related to atriangle prediction mode from the bitstream.

FIG. 22 illustrates an example of a syntax structure for parsinginformation related to a triangle prediction mode, according to anembodiment.

In S2201, the entropy decoder 2110 determines whether a prediction modeof a current mode is a regular merge mode. The regular merge mode refersto a mode in which a merge list including motion vectors of pre-encodedor pre-decoded blocks is generated to determine a motion vector of acurrent block, and then one of the motion vectors included in the mergelist is determined to be the motion vector of the current block. Whenthe prediction mode of the current mode is the regular merge mode, oneof motion vectors included in a merge list may be selected, according toan index (merge_idx) indicating the motion vector of the current block,and a reconstructed block may be generated based on a prediction blockindicated by the selected motion vector. The regular merge mode isdifferent from the triangle prediction mode, in that a current block isnot split into two triangular partitions.

In S2202, when the prediction mode of the current mode is the regularmerge mode, the entropy decoder 2110 obtains, from a bitstream, a flag(mmvd_merge_flag) indicating whether a prediction mode of a currentblock is the merge mode using a differential motion vector.

In S2203, when the prediction mode of the current block is the mergemode using a differential motion vector, the entropy decoder 2110obtains, from the bitstream, information (mmvd_cand_flag) indicating oneof the motion vectors included in the merge list, and obtains, from thebitstream, variation distance information (mmvd_distance_idx) andvariation direction information (mmvd_direction_idx) as informationindicating a differential motion vector. The prediction decoder 2130reconstructs the current block by using mmvd_cand_flag,mmvd_distance_idx, and mmvd_direction_idx, according to the merge modeusing a differential motion vector.

In S2204, when the prediction mode of the current block is not the mergemode using a differential motion vector, that is, when the predictionmode of the current block is the regular merge mode, the entropy decoder2110 obtains, from the bitstream, information (merge_idx) indicating oneof the motion vectors included in the merge list. The prediction decoder2130 reconstructs the current block by using merge_idx, according to theregular merge mode.

In S2205, the entropy decoder 2110 determines whether values of aplurality of variables (sps_ciip_enabled_flag,sps_triangle_enabled_flag, MaxNumTriangleMergeCand, silce_type, andcu_skip_flag) satisfy a preset condition. Also, the entropy decoder 2110determines whether a result of comparison between a size of the currentblock and a first threshold value, and a result of comparison betweenthe size of the current block and a second threshold value satisfy thepreset condition. In particular, according to A condition, when a valueobtained by multiplying a width (cbWidth) of the current block by aheight (cbHeight) of the current block is equal to or greater than 64,and both the width (cbWidth) and the height (cbHeight) of the currentblock are smaller than 128, in S2206, the entropy decoder 2110 obtains,from the bitstream, a flag (ciip_flag) indicating whether the predictionmode of the current block is an inter-intra combination mode. When theprediction mode of the current block is the inter-intra combinationmode, the prediction decoder 2130 reconstructs the current block bycombining a prediction block obtained in a reference image with aprediction block obtained in a current image according to theinter-intra combination mode.

In S2207, when the prediction mode of the current block is not theinter-intra combination mode, the entropy decoder 2110 obtains, from thebitstream, current block split shape information(merge_triangle_split_dir) and information (merge_triangle_idx0,merge_triangle_idx1) indicating a motion vector to be used as a motionvector of triangular partitions from among motion vectors included in amerge list for the triangle prediction mode, as information related to atriangle prediction mode.

The current block split shape information may indicate whether to splitthe current block from its upper-left corner toward its lower-rightcorner or whether to split the current block from its upper-right cornertoward its lower-left corner.

In FIG. 22 , according to a condition by which information related to atriangle prediction mode (merge_triangle_split_dir, merge_triangle_idx0,merge_triangle_idx1) is not obtained from the bitstream, first, inS2202, when the prediction mode of the current block is the merge modeusing a differential motion vector, the information related to atriangle prediction mode is not obtained from the bitstream. Also, inS2205, when the value obtained by multiplying the width of the currentblock by the height of the current block is smaller than 64, the widthof the current block is equal to or greater than 128, or the height ofthe current block is equal to or greater than 128, the informationrelated to a triangle prediction mode is not obtained from thebitstream. Also, in S2207, when the prediction mode of the current blockis the inter-intra combination mode, the information related to atriangle prediction mode is not obtained from the bitstream.

Hereinafter, a method by which the prediction decoder 2130 reconstructsa current block according to the triangle prediction mode, when aprediction mode of the current block is the triangle prediction mode andthe entropy decoder 2110 obtains information related to a triangleprediction mode from a bitstream, will now be described with referenceto FIGS. 23 to 27 .

FIG. 23 is a diagram for describing a merge list generation method in aregular merge mode.

In an embodiment, when a prediction mode of a current block 2310 is atriangle prediction mode, the prediction decoder 2130 may generate amerge list for the regular merge mode according to the merge listgeneration method in the regular merge mode, and may determine a mergelist for the triangle prediction mode by using the merge list for theregular merge mode.

In an embodiment, the prediction decoder 2130 may determine the mergelist for the regular merge mode to be the merge list for the triangleprediction mode without a change.

In another embodiment, the prediction decoder 2130 may determine themerge list for the triangle prediction mode by modifying the merge listfor the regular merge mode. In this regard, the fact that the merge listfor the regular merge mode is modified may indicate that an order ofmotion vectors included in the merge list for the regular merge mode maybe changed, some motion vectors may be excluded, or a new motion vectorthat did not exist in the merge list is added.

First, a method of generating the merge list for the regular merge modewill now be described.

The prediction decoder 2130 may generate a merge list including motionvectors of blocks that are available from among spatial blocks beingspatially related to the current block 2310 and temporal blocks beingtemporally related to the current block 2310. The spatial blocks and thetemporal blocks may include blocks that are decoded before the currentblock 2310.

Referring to FIG. 23 , the temporal block may include at least one of ablock (Col) co-located with respect to the current block 2310 in areference image that has a picture order count (POC) different from aPOC of the current block 2310, and a block (Br) being spatially adjacentto the co-located block (Col). The block (Br) may be located in thelower right side to the block (Col) that is co-located with respect tothe current block 2310. The block (Col) co-located with respect to thecurrent block 2310 may be a block including a pixel that corresponds toa center pixel in the current block 2310 and is from among pixelsincluded in the reference image.

The spatial block being spatially related to the current block 2310 mayinclude at least one of a lower-left corner block A0, a lower-left blockA1, an upper-right corner block B0, an upper-right block B1, and anupper-left corner block B2.

Locations of the temporal blocks and the spatial blocks shown in FIG. 23are merely an example, and in another embodiment, locations and thenumber of temporal blocks and spatial blocks may vary.

The prediction decoder 2130 may determine blocks to be available, theblocks being inter predicted from among the temporal blocks and thespatial blocks. The prediction decoder 2130 may add, to the merge list,motion vectors of the available blocks according to a predeterminedorder. When a motion vector of a certain available block is equal to amotion vector previously included in the merge list, the motion vectorof the certain available block may not be included in the merge list.

When the number of motion vectors included in the merge list is smallerthan a preset number, the prediction decoder 2130 may generate a newmotion vector by combining motion vectors included in the merge list andmay add the generated motion vector to the merge list. When the numberof motion vectors included in the merge list is smaller than a presetnumber, the prediction decoder 2130 may add zero vectors to the mergelist until the number of motion vectors included in the merge listreaches the preset number.

When generation of the merge list for the regular merge mode iscompleted, the prediction decoder 2130 may determine the merge list forthe regular merge mode to be the merge list for the triangle predictionmode, and may select a motion vector to be used as a motion vector oftriangular partitions from among the motion vectors included in themerge list, based on information related to a triangle prediction mode.

In an embodiment, when generation of the merge list for the regularmerge mode is completed, the prediction decoder 2130 may determine themerge list for the triangle prediction mode by modifying the merge listfor the regular merge mode, and may select a motion vector to be used asa motion vector of triangular partitions from among the motion vectorsincluded in the merge list, based on the information related to atriangle prediction mode.

A method of determining the merge list for the triangle prediction modeby modifying the merge list for the regular merge mode will now bedescribed with reference to FIGS. 24 and 25 .

FIGS. 24 and 25 illustrate examples for describing a method ofgenerating the merge list for the triangle prediction mode from themerge list for the regular merge mode.

First, in FIG. 24 , a merge list shown in the left is for the regularmerge mode, in which B1, B0, A0, and B2 represent motion vectors ofavailable spatial blocks, and Col represents a motion vector of anavailable temporal block.

The prediction decoder 2130 adds a uni-direction motion vector fromamong motion vectors included in the merge list to the merge list forthe triangle prediction mode. The uni-direction motion vector refers toa motion vector that indicates a block in a reference image included inList 0 or indicates a block in a reference image included in List 1. Incontrast, a bi-direction motion vector refers to a motion vector thatindicates a block in a reference image included in List 0 and a block ina reference image included in List 1.

When B1, A0, B2, and Col from among B1, B0, A0, B2, and Col areuni-direction motion vectors, the prediction decoder 2130 adds B1, A0,B2, and Col to the merge list for the triangle prediction mode as shownin the right of FIG. 24 . When the number of motion vectors included inthe merge list for the triangle prediction mode is smaller than a presetnumber (e.g., 5), the prediction decoder 2130 generates a newbi-direction motion vector by combining motion vectors, which arealready included in the merge list, according to a predeterminedcriterion, and adds the generated motion vector to the merge list.Referring to FIG. 24 , it is apparent that B1+A0 generated by combiningB1 and A0 is added as a last candidate to the merge list.

Next, referring to FIG. 25 , the prediction decoder 2130 may generatethe merge list for the triangle prediction mode by considering only apredetermined number of motion vectors from among motion vectorsincluded in the merge list for the regular merge mode. For example, togenerate the merge list for the triangle prediction mode, the predictiondecoder 2130 may use only four motion vectors in an order that they areincluded in the merge list from among five motion vectors included inthe merge list for the regular merge mode. Accordingly, the predictiondecoder 2130 adds a uni-direction motion vector to the merge list forthe triangle prediction mode, wherein the uni-direction motion vector isfrom among B1, B0, A0, and B2 that are four motion vectors included inthe merge list for the regular merge mode. When B1, A0, and B2 fromamong B1, B0, A0, and B2 are uni-direction motion vectors, as shown inthe right of FIG. 25 , the prediction decoder 2130 adds B1, A0, and B2to the merge list for the triangle prediction mode. Then, when thenumber of motion vectors included in the merge list for the triangleprediction mode is smaller than a preset number (e.g., 5), theprediction decoder 2130 generates a new bi-direction motion vector bycombining motion vectors, which are already included in the merge list,according to a predetermined criterion, and adds the generated motionvector to the merge list. Referring to FIG. 25 , it is apparent thatB1+A0 generated by combining B1 and A0, and B1+B2 generated by combiningB1 and B2 are added after B2 to the merge list for the triangleprediction mode.

With reference to FIGS. 24 and 25 , in a case where a new motion vector(B1+A0, B1+B2, etc.) generated as a result of combination ofuni-direction motion vectors is added to the merge list for the triangleprediction mode, only when the new motion vector is not equal to amotion vector pre-added to the merge list, the prediction decoder 2130may add the new motion vector to the merge list for the triangleprediction mode.

In this regard, in an embodiment, only when the new motion vector is notequal to all motion vectors pre-added to the merge list, the predictiondecoder 2130 may add the new motion vector to the merge list for thetriangle prediction mode.

However, determination of whether the new motion vector is not equal toall motion vectors pre-added to the merge list increasesencoding/decoding complexity, and thus, in another embodiment, theprediction decoder 2130 may add the new motion vector to the merge listfor the triangle prediction mode when the new motion vector is not equalto a motion vector that is most recently added to the merge list.

When generation of the merge list for the triangle prediction mode iscompleted, the prediction decoder 2130 determines a motion vector oftriangular partitions, based on information related to a triangleprediction mode. In detail, the prediction decoder 2130 may obtaininformation (e.g., an index) indicating a motion vector to be used asthe motion vector of the triangular partitions from among motion vectorsincluded in the merge list, and may determine the motion vectorindicated by the information to be the motion vector of the triangularpartitions. For example, according to descriptions with reference toFIG. 25 , when an index indicating the motion vector of the triangularpartitions indicates 0 and 1, the prediction decoder 2130 may determineB1 to be a motion vector of one triangular partition and may determineA0 to be a motion vector of another triangular partition.

When motion vectors of triangular partitions are determined, theprediction decoder 2130 determines prediction blocks indicated by themotion vectors in a reference image.

FIG. 26 is a diagram for describing a method of determining predictionblocks 2612 and 2614 corresponding to two triangular partitions 2312 and2314 split from the current block 2310. As illustrated in FIG. 26 , theprediction decoder 2130 may obtain a first prediction block 2612indicated by a motion vector mv1 of a first triangular partition 2312and a second prediction block 2614 indicated by a motion vector mv2 of asecond triangular partition 2314.

FIG. 26 illustrates that the first prediction block 2612 and the secondprediction block 2614 are included in one reference image, but this ismerely an example, and thus, the first prediction block 2612 and thesecond prediction block 2614 may be respectively located in differentreference images.

When the prediction blocks 2612 and 2614 corresponding to the triangularpartitions 2312 and 2314 are obtained, the prediction decoder 2130generates a final prediction block by combining the prediction blocks2612 and 2614. This will now be described with reference to FIG. 27 .

FIG. 27 is a diagram for describing a method of generating a finalprediction block 2710 by combining the prediction blocks 2612 and 2614corresponding to the two triangular partitions 2312 and 2314.

The prediction decoder 2130 may generate the final prediction block 2710by weighted summing first sample values P1 included in the firstprediction block 2612 and second sample values P2 included in the secondprediction block 2614 which correspond to the first triangular partition2312 and the second triangular partition 2314.

Referring to FIG. 27 , when the current block 2310 is split into twotriangular partitions along its upper-left corner and its lower-rightcorner, first sample values P1 and second sample values P2 located on aboundary 2315 are summed by applying weights (4/8, 4/8) thereto, thefirst sample values P1 and the second sample values P2 being from amongthe first sample values P1 included in the first prediction block 2612and the second sample values P2 included in the second prediction block2614. Then, a higher weight may be applied to first sample values P1 ina direction toward an upper-right corner from the boundary 2315, and ahigher weight may be applied to second sample values P2 in a directiontoward a lower-left corner from the boundary 2315. The first samplevalues P1 are allocated to samples adjacent to the upper-right cornerfrom among samples of the final prediction block 2710, and the secondsample values P2 are allocated to samples adjacent to the lower-leftcorner from among the samples of the final prediction block 2710.

With references to FIGS. 26 and 27 , a case is described, in which thecurrent block 2310 is split into the two triangular partitions withrespect to the upper-left corner and the lower-right corner. However,even when the current block 2310 is split into two triangular partitionswith respect to its upper-right corner and its lower-left corner, afinal prediction block may be generated in a same manner.

FIG. 28 is a flowchart of an image decoding method according to anembodiment.

In operation S2810, the image decoding apparatus 2100 obtains, from abitstream, information related to a triangle prediction mode for acurrent block split from a current image.

When a result of comparison between a size of the current block and afirst threshold value satisfies a preset condition, the image decodingapparatus 2100 may obtain the information related to a triangleprediction mode for the current block from the bitstream. In detail,when a width of the current block is smaller than the first thresholdvalue and a height of the current block is smaller than the firstthreshold value, the image decoding apparatus 2100 may obtain theinformation related to a triangle prediction mode from the bitstream. Incontrast, when a width of the current block is equal to or greater thanthe first threshold value or a height of the current block is equal toor greater than the first threshold value, the image decoding apparatus2100 may obtain the information related to a triangle prediction modefrom the bitstream.

In an embodiment, the image decoding apparatus 2100 may compare a sizeof the current block with a second threshold value, and when a result ofthe comparison satisfies the preset condition, the image decodingapparatus 2100 may obtain the information related to a triangleprediction mode for the current block from the bitstream. In detail,when a value obtained by multiplying a width of the current block by aheight of the current block is equal to or greater than the secondthreshold value, the image decoding apparatus 2100 may obtain theinformation related to a triangle prediction mode from the bitstream. Incontrast, when a value obtained by multiplying a width of the currentblock by a height of the current block is smaller than the secondthreshold value, the image decoding apparatus 2100 may not obtain theinformation related to a triangle prediction mode from the bitstream.

When a prediction mode of the current block is not the inter-intracombination mode, the image decoding apparatus 2100 may obtain theinformation related to a triangle prediction mode for the current blockfrom the bitstream, and in contrast, when the prediction mode of thecurrent block is the inter-intra combination mode, the image decodingapparatus 2100 may not obtain the information related to a triangleprediction mode for the current block from the bitstream.

Also, when the prediction mode of the current block is the merge modeusing a differential motion vector, the image decoding apparatus 2100may not obtain the information related to a triangle prediction mode forthe current block from the bitstream. In contrast, when the predictionmode of the current block is not the merge mode using a differentialmotion vector, the image decoding apparatus 2100 may obtain theinformation related to a triangle prediction mode for the current blockfrom the bitstream.

The information related to a triangle prediction mode may include atleast one of information indicating whether the triangle prediction modeis to be applied to the current block, current block split shapeinformation, and information indicating a motion vector of triangularpartitions. The current block split shape information may indicatewhether to split the current block along a boundary connecting anupper-left corner and a lower-right corner of the current block orwhether to split the current block along a boundary connecting anupper-right corner and a lower-left corner of the current block.

In operation S2820, the image decoding apparatus 2100 generates a mergelist for the triangle prediction mode, according to the merge listgeneration method in a regular merge mode in which the current block isreconstructed without being split into triangular partitions.

In an embodiment, the image decoding apparatus 2100 may determine themerge list for the regular merge mode to be the merge list for thetriangle prediction mode without a change

In another embodiment, the image decoding apparatus 2100 may determinethe merge list for the triangle prediction mode by modifying the mergelist for the regular merge mode. In this regard, the fact that the mergelist for the regular merge mode is modified may indicate that an orderof motion vectors included in the merge list for the regular merge modemay be changed, some motion vectors may be excluded, or a new motionvector that did not exist in the merge list is added.

The merge list generation method in a regular merge mode may indicate amethod of generating a merge list including motion vectors of blocksthat are available from among spatial blocks being spatially related tothe current block and temporal blocks being temporally related to thecurrent block.

In operation S2830, the image decoding apparatus 2100 splits the currentblock into two triangular partitions, according to the informationrelated to a triangle prediction mode. The image decoding apparatus 2100may split the current block from an upper-left corner of the currentblock toward a lower-right corner of the current block or may split thecurrent block from an upper-right corner of the current block toward alower-left corner of the current block.

In operation S2840, the image decoding apparatus 2100 selects a motionvector for the two triangular partitions according to informationindicating a motion vector among motion vectors included in the mergelist for the triangle prediction mode, the information being included inthe information related to a triangle prediction mode.

In operation S2850, the image decoding apparatus 2100 obtains, from areference image, prediction blocks indicated by the motion vector forthe two triangular partitions.

In operation S2860, the image decoding apparatus 2100 combines theprediction blocks corresponding to the two triangular partitions. Then,the image decoding apparatus 2100 reconstructs the current block, basedon a final prediction block generated as a result of the combination ofthe prediction blocks.

In an embodiment, the image decoding apparatus 2100 may determine thefinal prediction block to be a reconstructed block. In anotherembodiment, the image decoding apparatus 2100 may combine the finalprediction block with a residual block obtained based on informationincluded in the bitstream, and may determine a combination block to be areconstructed block.

FIG. 29 is a block diagram of a configuration of the image encodingapparatus 2900 according to an embodiment.

Referring to FIG. 29 , the image encoding apparatus 2900 may include aprediction encoder 2910 and an entropy encoder 2930. The predictionencoder 2910 and the entropy encoder 2930 may respectively correspond tothe encoder 220 and the bitstream generator 210 shown in FIG. 2 . Also,the prediction encoder 2910 and the entropy encoder 2930 mayrespectively correspond to the prediction encoder 2015 and the entropyencoder 2025 shown in FIG. 20 .

The prediction encoder 2910 and the entropy encoder 2930 according to anembodiment may be implemented as at least one processor. The imageencoding apparatus 2900 may include one or more memories (not shown) forstoring input and output data of the prediction encoder 2910 and theentropy encoder 2930. Also, the image encoding apparatus 2900 mayinclude a memory controller (not shown) for controlling data inputs andoutputs of the memory (not shown).

The prediction encoder 2910 determines a prediction mode of a currentblock. The prediction encoder 2910 may determine the prediction mode ofthe current block to be a regular merge mode, a merge mode using adifferential motion vector, an inter-intra combination mode, a triangleprediction mode, or an intra mode.

The prediction encoder 2910 may encode the current block according tothe triangle prediction mode. In particular, when the prediction mode ofthe current block is determined to be the triangle prediction mode, theprediction encoder 2910 generates a merge list for the triangleprediction mode. A method of generating the merge list for the triangleprediction mode is same as that described with reference to FIGS. 23 to25 , and thus, detailed descriptions thereof are not provided here. Theprediction encoder 2910 splits the current block into two triangularpartitions, and selects a motion vector to be used as a motion vector ofthe two triangular partitions from among motion vectors included in themerge list. The prediction encoder 2910 signals, to the image decodingapparatus 2100, information related to a triangle prediction mode, indetail, information indicating the motion vector of the two triangularpartitions and information indicating a split shape of the currentblock.

In a certain case, encoding the current block in the triangle predictionmode may not be good in terms of coding efficiency, and in this case,when the information related to a triangle prediction mode is includedin a bitstream, the number of unnecessary bits may increase.

Accordingly, in an embodiment, before the information related to atriangle prediction mode is generated, whether it is appropriate toencode the current block in the triangle prediction mode may be firstdetermined based on a preset condition, and then, whether to generatethe information related to a triangle prediction mode may be adaptivelydetermined according to a result of the determination.

In the first embodiment, the prediction encoder 2910 may compare a sizeof the current block with a first threshold value, and when a result ofthe comparison satisfies the preset condition, the prediction encoder2910 may determine the prediction mode of the current block to be thetriangle prediction mode. For example, when a height of the currentblock is smaller than the first threshold value and a width of thecurrent block is smaller than the first threshold value, the predictionencoder 2910 may determine the prediction mode of the current block tobe the triangle prediction mode. In contrast, when a height or a widthof the current block is equal to or greater than the first thresholdvalue, the prediction encoder 2910 may determine the prediction mode ofthe current block to be a mode other than the triangle prediction mode.Also, for example, when a height or a width of the current block issmaller than the first threshold value, the prediction encoder 2910 maydetermine the prediction mode of the current block to be the triangleprediction mode. In contrast, when both a height and a width of thecurrent block are equal to or greater than the first threshold value,the prediction encoder 2910 may determine the prediction mode of thecurrent block to be a mode other than the triangle prediction mode.

The first embodiment is provided to restrict that the triangleprediction mode is to be applied to a large-size current block. Becausesizes of two triangular partitions obtained from the large-size currentblock are large, sameness between a final prediction block and thecurrent block may be decreased, compared to a case where the currentblock is quad split or ternary split. Accordingly, in the firstembodiment, it is determined that the triangle prediction mode is to notbe applied to the current block when the size of the current block isequal to or greater than the first threshold value, and the informationrelated to a triangle prediction mode may not be generated.

In the second embodiment, the prediction encoder 2910 may compare a sizeof the current block with a second threshold value, and when a result ofthe comparison satisfies the preset condition, the prediction encoder2910 may determine the prediction mode of the current block to be thetriangle prediction mode. For example, when a value obtained bymultiplying a height of a current block by a width of the current blockis equal to or greater than the second threshold value, the predictionencoder 2910 may determine the prediction mode of the current block tobe the triangle prediction mode. In contrast, when a value obtained bymultiplying a height of the current block by a width of the currentblock is smaller than the second threshold value, the prediction encoder2910 may determine the prediction mode of the current block to be a modeother than the triangle prediction mode. Also, for example, when both aheight and a width of the current block are equal to or greater than thesecond threshold value, the prediction encoder 2910 may determine theprediction mode of the current block to be the triangle prediction mode.In contrast, when a height or a width of the current block is smallerthan the second threshold value, the prediction encoder 2910 maydetermine the prediction mode of the current block to be a mode otherthan the triangle prediction mode.

The second threshold value may be smaller than the first threshold valuedescribed with reference to the first embodiment. For example, the firstthreshold value may be 128, and the second threshold value may be 64. Inanother embodiment, the second threshold value and the first thresholdvalue may be identical. For example, both the first threshold value andthe second threshold value may be 64.

The second embodiment is provided to restrict that the triangleprediction mode is to be applied to a small-size current block. When acurrent block of a very small size is split into two triangularpartitions, complexity of an encoding and decoding process is large,compared to its coding efficiency. Accordingly, in the secondembodiment, when a size of the current block is smaller than the secondthreshold value, it may be determined that the triangle prediction modeis to not be applied to the current block, and the information relatedto a triangle prediction mode may not be generated.

In the third embodiment, when the prediction mode of the current blockis not the inter-intra combination mode, the prediction encoder 2910 maydetermine the prediction mode of the current block to be the triangleprediction mode. In contrast, when the prediction mode of the currentblock is the inter-intra combination mode, the prediction encoder 2910may not determine whether to encode the current block in the triangleprediction mode.

In a conventional case where a current block is encoded without beingsplit or the current block is split and then encoded, according to aninter mode, when a cost (e.g., a rate-distortion cost) is high, theinter-intra combination mode may be applied as a prediction mode of thecurrent block. That is, the fact that the inter-intra combination modeis applied to the current block may indicate that a coding efficiency isnot good even when the current block is partitioned, such that, onlywhen the prediction mode of the current block is not the inter-intracombination mode, the prediction encoder 2910 may determine theprediction mode of the current block to be the triangle prediction mode,and may generate the information related to a triangle prediction mode.

In the fourth embodiment, when the prediction mode of the current blockis the merge mode using a differential motion vector, the predictionencoder 2910 may not determine whether to encode the current blockaccording to the triangle prediction mode. In contrast, when theprediction mode of the current block is not the merge mode using adifferential motion vector, the prediction encoder 2910 may determinethe prediction mode of the current block to be the triangle predictionmode.

The fact that the merge mode using a differential motion vector isapplied to a current block indicates that efficiency is good when thecurrent block is encoded/decoded by using a motion vector included inthe merge list without a need to partition the current block.Accordingly, when the merge mode using a differential motion vector isapplied to the current block, the prediction encoder 2910 may notdetermine whether to encode the current block in the triangle predictionmode.

The prediction encoder 2910 may combine conditions described above withreference to the first embodiment, the second embodiment, the thirdembodiment, and the fourth embodiment so as to determine whether toencode the current block in the triangle prediction mode.

For example, when the result of the comparison between the size of thecurrent block and the first threshold value, and the result of thecomparison between the size of the current block and the secondthreshold value satisfy the preset condition, the prediction encoder2910 may determine the prediction mode of the current block to be thetriangle prediction mode. For example, when the height and the width ofthe current block are smaller than the first threshold value, and aresult obtained by multiplying the height of the current block by thewidth of the current block is equal to or greater than the secondthreshold value, the prediction encoder 2910 may determine theprediction mode of the current block to be the triangle prediction mode.

As another example, the prediction encoder 2910 may determine whether toencode the current block in the triangle prediction mode, according tothe result of the comparison between the size of the current block andthe first threshold value, and whether the prediction mode of thecurrent block is the inter-intra combination mode. For example, when theheight and the width of the current block are smaller than the firstthreshold value, and the prediction mode of the current block is not theinter-intra combination mode, the prediction encoder 2910 may determinethe prediction mode of the current block to be the triangle predictionmode.

As another example, the prediction encoder 2910 may determine whether toencode the current block in the triangle prediction mode, according tothe result of the comparison between the size of the current block andthe first threshold value, and whether the prediction mode of thecurrent block is the merge mode using a differential motion vector. Forexample, when the height or the width of the current block is equal toor greater than the first threshold value, or the prediction mode of thecurrent block is the merge mode using a differential motion vector, theprediction encoder 2910 may not determine whether to encode the currentblock in the triangle prediction mode.

As another example, the prediction encoder 2910 may determine whether toencode the current block in the triangle prediction mode, according tothe result of the comparison between the size of the current block andthe first threshold value, the result of the comparison between the sizeof the current block and the second threshold value, and whether theprediction mode of the current block is the inter-intra combinationmode. For example, when the height and the width of the current blockare smaller than the first threshold value, the value obtained bymultiplying the height of the current block by the width of the currentblock is equal to or greater than the second threshold value, and theprediction mode of the current block is not the inter-intra combinationmode, the prediction encoder 2910 may determine the prediction mode ofthe current block to be the triangle prediction mode.

In an embodiment, the prediction encoder 2910 may generate syntaxelements (mmvd_merge_flag, mmvd_cand_flag, mmvd_distance_idx,mmvd_direction_idx, merge_idx, ciip_flag, merge_triangle_split_dir,merge_triangle_idx0, and merge_triangle_idx1) according to the syntaxstructure shown in FIG. 22 . The syntax elements may be entropy encodedby the entropy encoder 2930 and then may be included in a bitstream.

The entropy encoder 2930 may generate the bitstream by entropy encodingvalues corresponding to the syntax elements. The entropy encoder 2930may encode the values corresponding to the syntax elements, according toCABAC.

The bitstream may include a plurality of pieces of information to beused in reconstruction of a current block. The current block may be ablock generated by being split from an image according to a treestructure, and may correspond to a block such as a largest coding unit,a coding unit, or a transform unit, etc.

The bitstream that corresponds to at least one level among a sequenceparameter set, a picture parameter set, a video parameter set, a sliceheader, and a slice segment header may include block shape informationand/or split shape mode information, and the image decoding apparatus2100 may determine the current block in a current image, based on theblock shape information and/or the split shape mode information.

The bitstream may include information indicating a prediction mode ofthe current block. The prediction mode of the current block may includea regular merge mode, a merge mode using a differential motion vector,an inter-intra combination mode, a triangle prediction mode, or an intramode.

Also, when the prediction mode of the current block is determined to bethe triangle prediction mode, the bitstream may include informationrelated to a triangle prediction mode. The information related to atriangle prediction mode may include at least one of informationindicating whether the prediction mode of the current block is thetriangle prediction mode, split shape information for splitting thecurrent block into two triangular partitions, and information indicatinga motion vector of the two triangular partitions.

FIG. 30 is a flowchart of an image encoding method according to anembodiment.

In S3010, the image encoding apparatus 2900 determines a prediction modeof a current block to be a triangle prediction mode, the current blockbeing split from a current image.

When a result of comparison between a size of the current block and afirst threshold value satisfies a preset condition, the image encodingapparatus 2900 may determine the prediction mode of the current block tobe the triangle prediction mode. In detail, when a width of the currentblock is smaller than the first threshold value and a height of thecurrent block is smaller than the first threshold value, the imageencoding apparatus 2900 may determine the prediction mode of the currentblock to be the triangle prediction mode. In contrast, when a width ofthe current block is equal to or greater than the first threshold valueor a height of the current block is equal to or greater than the firstthreshold value, the image encoding apparatus 2900 may determine theprediction mode of the current block to be a mode other than thetriangle prediction mode.

In an embodiment, the image encoding apparatus 2900 may compare a sizeof the current block with a second threshold value, and when a result ofthe comparison satisfies the preset condition, the image encodingapparatus 2900 may determine the prediction mode of the current block tobe the triangle prediction mode. In detail, when a value obtained bymultiplying a width of the current block by a height of the currentblock is equal to or greater than the second threshold value, the imageencoding apparatus 2900 may determine the prediction mode of the currentblock to be the triangle prediction mode. In contrast, when a valueobtained by multiplying a width of the current block by a height of thecurrent block is smaller than the second threshold value, the imageencoding apparatus 2900 may determine the prediction mode of the currentblock to be a mode other than the triangle prediction mode.

When the prediction mode of the current block is not the inter-intracombination mode, the image encoding apparatus 2900 may determine theprediction mode of the current block to be the triangle prediction mode,and in contrast, when the prediction mode of the current block is theinter-intra combination mode, the image encoding apparatus 2900 may notdetermine whether to encode the current block in the triangle predictionmode.

Also, when the prediction mode of the current block is the merge modeusing a differential motion vector, the image encoding apparatus 2900may not determine whether to encode the current block in the triangleprediction mode. In contrast, when the prediction mode of the currentblock is not the merge mode using a differential motion vector, theimage encoding apparatus 2900 may determine the prediction mode of thecurrent block to be the triangle prediction mode.

In S3020, the image encoding apparatus 2900 generates a merge list forthe triangle prediction mode, according to a merge list generationmethod in a regular merge mode in which a current block is encodedwithout being split into triangular partitions.

In an embodiment, the image encoding apparatus 2900 may determine themerge list for the regular merge mode to be the merge list for thetriangle prediction mode without a change

In another embodiment, the image encoding apparatus 2900 may determinethe merge list for the triangle prediction mode by modifying the mergelist for the regular merge mode. In this regard, the fact that the mergelist for the regular merge mode is modified may indicate that an orderof motion vectors included in the merge list for the regular merge modemay be changed, some motion vectors may be excluded, or a new motionvector that did not exist in the merge list is added.

The merge list generation method in the regular merge mode may indicatea method of generating a merge list including motion vectors of blocksthat are available from among spatial blocks being spatially related toa current block and temporal blocks being temporally related to thecurrent block.

In S3030, the image encoding apparatus 2900 splits the current blockinto two triangular partitions. The image encoding apparatus 2900 maysplit the current block from an upper-left corner of the current blocktoward a lower-right corner of the current block or may split thecurrent block from an upper-right corner of the current block toward alower-left corner of the current block.

In operation S3040, the image encoding apparatus 2900 selects a motionvector to be used as a motion vector of the two triangular partitionsfrom among motion vectors included in the merge list for the triangleprediction mode. The image encoding apparatus 2900 may select a motionvector among motion vectors included in the merge list that causes asmallest cost (e.g., a rate-distortion cost) for the two triangularpartitions.

In operation S3050, the image encoding apparatus 2900 generates abitstream including information related to a triangle prediction mode.

The information related to a triangle prediction mode may include atleast one of information indicating whether the triangle prediction modeis to be applied to the current block, current block split shapeinformation, and information indicating a motion vector of triangularpartitions. The current block split shape information may indicatewhether to split the current block along a boundary connecting anupper-left corner and a lower-right corner of the current block orwhether to split the current block along a boundary connecting anupper-right corner and a lower-left corner of the current block.

Meanwhile, the embodiments of the disclosure may be written as programsthat are executable on a computer, and the programs may be stored in amedium.

The medium may continuously store the computer-executable programs ormay temporarily store the computer-executable programs for execution ordownloading. Also, the medium may be any one of various recording mediaor storage media in which a single piece or plurality of pieces ofhardware are combined, and the medium is not limited to those directlyconnected to a certain computer system, but may be distributed over anetwork. Examples of the medium include magnetic media such as a harddisk, a floppy disk, and a magnetic tape, optical recording media suchas compact disc-read only memory (CD-ROM) and a digital versatile disc(DVD), magneto-optical media such as floptical disk, read only memory(ROM), radom access memory (RAM), a flash memory, etc., which areconfigured to store program instructions. Also, other examples of themedium include recording media and storage media managed by applicationstores distributing applications or by websites, servers, and the likesupplying or distributing other various types of software.

While one or more embodiments of the disclosure are described in detailwith reference to examplary embodiments above, it will be understood byone of ordinary skill in the art that the disclosure is not limited tothe embodiments, and various changes in form and details may be madetherein without departing from the spirit and scope of the disclosure.

1. An image decoding method performed by an image decoding apparatus,the image decoding method comprising: when a size of a current block isequal to or greater than a predetermined value, obtaining informationindicating whether an inter-intra combination mode is applied to thecurrent block; when the information indicates that the inter-intracombination mode is not applied to the current block, obtaining, from abitstream, partition shape information for the current block, firstmotion vector related information for a first partition and secondmotion vector related information for a second partition; obtaining afirst prediction sample using a motion vector of a first candidate blockindicated by the first motion vector related information among aplurality of candidate blocks included in a merge list; obtaining asecond prediction sample using a motion vector of a second candidateblock indicated by the second motion vector related information amongthe plurality of candidate blocks included in the merge list;determining a weight value for the first prediction sample and thesecond prediction sample using the partition shape information;obtaining a third prediction sample by combining the first predictionsample and the second prediction sample using the weight value; andreconstructing the current block by using the third prediction sample.2. An image decoding apparatus comprising: an entropy decoder configuredto, when a size of a current block is equal to or greater than apredetermined value, obtain information indicating whether aninter-intra combination mode is applied to the current block, and whenthe information indicates that the inter-intra combination mode is notapplied to the current block, obtain, from a bitstream, partition shapeinformation for the current block, first motion vector relatedinformation for a first partition and second motion vector relatedinformation for a second partition; and a prediction decoder configuredto obtain a first prediction sample using a motion vector of a firstcandidate block indicated by the first motion vector related informationamong a plurality of candidate blocks included in a merge list, obtain asecond prediction sample using a motion vector of a second candidateblock indicated by the second motion vector related information amongthe plurality of candidate blocks included in the merge list, determinea weight value for the first prediction sample and the second predictionsample using the partition shape information, obtain a third predictionsample by combining the first prediction sample and the secondprediction sample by using the weight value, and reconstruct the currentblock by using the third prediction sample.
 3. An image encoding methodperformed by an image encoding apparatus, the image encoding methodcomprising: when a size of a current block is equal to or greater than apredetermined value, determining whether an inter-intra combination modeis applied to the current block; when it is determined that theinter-intra combination mode is not applied to the current block,determining a partition shape for the current block, and selecting,among a plurality of candidate blocks comprised in a merge list, a firstcandidate block for a first partition and a second candidate block for asecond partition; and generating a bitstream comprising informationindicating whether the inter-intra combination mode is applied to thecurrent block, first motion vector related information indicating thefirst candidate block, second motion vector related informationindicating the second candidate block, and partition shape informationfor the current block, wherein the current block corresponds to a thirdprediction sample obtained by combining a first prediction sample and asecond prediction sample, the first prediction sample is determinedbased on a motion vector of the first candidate block, and the secondprediction sample is determined based on a motion vector of the secondcandidate block, and the first prediction sample and the secondprediction sample are combined based on a weight value determined usingthe partition shape information.
 4. A computer-readable medium forrecording a bitstream, the bitstream comprising: information indicatingwhether an inter-intra combination mode is applied to a current block;first motion vector related information indicating a first candidateblock; second motion vector related information indicating a secondcandidate block; and partition shape information for the current block,wherein when a size of the current block is equal to or greater than apredetermined value, the information indicating whether the inter-intracombination mode is applied to the current block is comprised in thebitstream, wherein when the information indicating whether theinter-intra combination mode is applied to the current block is generateto indicate that the inter-intra combination mode is not applied to thecurrent block, the partition shape information, the first motion vectorrelated information and the second motion vector related information arecomprised in the bitstream, wherein the first candidate block for afirst partition and the second candidate block for a second partitionare selected among a plurality of candidate blocks comprised in a mergelist, wherein the current block corresponds to a third prediction sampleobtained by combining a first prediction sample and a second predictionsample, wherein the first prediction sample is determined based on amotion vector of the first candidate block, and the second predictionsample is determined based on a motion vector of the second candidateblock, and wherein the first prediction sample and the second predictionsample are combined based on a weight value determined using thepartition shape information.